[G]How to Mech them cry : Lyyna's Mech in HotS

18/06/2014 : Even though the post isn’t 100% finished, i consider i do have enough content to now post it, especially in order to start to fill it with community content and i want to have some feedback since the "skeleton" of it is done (Also, i do know that if i wait to post a “perfect” guide , i won’t ever post it, since i would want to edit every single sentence again and again and won’t ever be satisfied.. especially considering its huge size). What remains currently to do is to add a “spells” section, and a positioning/micro section. The TvP lategame section miss also a couple of sections (but it should be obvious while reading it), that’ll be added tomorrow. I do currently have a lots of time to write so don’t worry, that’ll be done. Anyway, first version !
19/06/2014 : Additions to the "TvP lategame" section, added a small replay pack, question "TvP : Why using thors in the midgame instead of going for tanks asap ?" added
01/07/2014 : More additions to everything. Planned map section won't be done until next season
08/07/2014 : Wording
27/07/2014 : Some formatting stuff, new replay pack
29/07/2014 : Some Cattlebruiser stuff, and more harassey stuff. Also started the gameplay logs section
19/10/2014 : Addition of new content about lategame ghosts TvZ. New replay pack. Suppression of the gameplay logs section (basically the content is repeated in individual guides)

A mainly factory based army/strategy, which still includes other (air, ghost) units (we can talk of specific subsets for this, like ghostmech or skymech, but the general “mech” concept still applies). This is here so i don’t get butchered by some people saying “YOU ARE NOT MAKING ONLY FACT UNITS THIS IS NO MECH”, like it happened on my WoL thread (funnily enough, it is perfectly fine for these people to say we’re playing “bio” versus protoss, like only marines/marauders/ghost, without any viking/medivac/mine/hellbat, right ?).

I do play a mainly defensive playstyle, focusing on staying alive as long as possible, and aiming at overpowering my opponent in the lategame with a superior positionning/army/control. But well, lately, i’ve also been working on more agressive playstyles (to be honest, more like “being less shy and trying to exploit weaknesses when i see them”).

Originally, because my apm were too low to play the since-long-standard bio/aggressive terran style popular in every matchups, and because i liked a lot the positioning-play created by the tank in BW. I wanted to play a tank-centric style, allowing me to use the fact my game sense, positionning, and theorycrafting were faaaaar beyond my mechanical skills (oh the irony). Nowadays… because i still hate bio play, and also because playing aggressive (besides harass) as mech became extremely hard in HotS : the threat of stuff like viper or mass muta or SH or overall stronger protoss midgame/lategame for example made it way more dangerous to leave my base in HotS, both because my army sometimes lacks some “punch power” compared to our opponent’s, and because of the threat of base races. Mech midgame haven’t changed much to balance these changes, and the biggest addition from HotS is in the lategame, the new raven, meaning it became way more reliable to play an overall defensive style instead of the old harass-into-timing based mech from WoL or the good old BW-like slow doom push. Mech starts to really become strong around 150+ supply, and considering the slow production for us / higher production and relatively easy access to anti-mech tech for every race, it means we now have to play defensive to reach your power peak

A really common misconception, born from the fact mech players tends to be really slow mech..anically (laugh, please, otherwise i’ll feel terrible), and from sometimes-popular easy-to-do big 2 / 3 bases mech timing/allins (even if they tend to get figured out easily, they still looks scary and requires enough scouting/deviation so that most players find them infuriating), making it kinda frustrating to a “noob who just sit on 3 bases and kills me with half my APM in 1 A move”. The fact is that mech (outside of these allin-ish timings, of course) requires quite a lot of non-control/apm related skills, the ability to metagame/anticipate well, to know when to cut corners, to position extremly well (you cannot stim and run if you put yourself in a bad spot with your tanks and thors . . .), and still requires a decent amount of mechanical skills, the macro has to be extremly precise, and even if some situations can be kinda microless (like an early-midgame battle with pure tanks versus pure roaches), especially in the lategame the micro/multitask required can be quite overwhelming (raven TvT wars ; as a sidenote, it is always extremly satisfying to win these versus bioplayers who taunted me all game long about my “no micro noob style”, and ends up losing 60 supply of clumped air units to 4 missiles - yes, while watching the battle/having the units selected…)

Marine : a terrible unit, that has some usage early game for defense, but that’s all. I heard they have some kind of attack/movement speed increase with some upgrade, but never bothered to really look into this
Ghost : a high cost, fragile unit, vulnerable to feedback, air units, or just “too-many-stuff-to-EMP-all-of-it” that can take out 40% of the protoss army health instantly, and deals easily with threatening things like immorta/HT/archon. It can be used as well in lategame TvT (rare) to fight ravens / BCs, and in TvZ to fight vipers/infestors heavy composition. Nukes are a possibility in all MUs but aren't my thing.
Hellion/hellbat : obviously, our core mineral dump. With the ability to freely transform from one to another, we should use both and not hesitate to switch between them. Hellions are good for scouting (even in the lategame, i usually keep 1-2 hellions with my army for this, in order to secure my army’s path/flanks), harassing/raiding (and actually, with hellbat mode, a 6-8 hellion patrol can take out quite a lot of defense), defending from harass, and decent in fights (actually, their AOE attack can often do more damage than hellbats versus melee units). Hellbats on the other hand are good at taking out nearly everything that come too close, and at tanking a tons of damage (especiallt with medivacs). Usually, we’ll want to have a lot (10+) of them in the midgame, and even if they’re the first combat unit we’ll replace (after scvs), in some situations it can be quite good to have some in the lategame (in TvP the buffer is always useful, and in TvZ a couple helps a lot versus any surprise zerglings production)
TvZ : +3 attack Hellbats one shot zerglings. For 2 supply, if we have a good simcity, we can get an invincible anti zergling defense for a base. We can chose to keep 2 in our main base / production area in the lategame for easy defense against runbys
TvP : if we can get close to them, and get a surround, hellions are surprisingly good versus stalkers in high numbers
Widow mine : honestly, this unit isn’t that good for mech in most situations. It tends to be quite random, to kill a lot of our units versus things like zerglings/chargelots, and is only effective for some early game defense (to be honest, for this, they can be quite amazing), emergency anti air, or some trolly mass mines style (which works decently if there is no AOE). July 2014 : with the recent up, even though i won't use it as a core unit still, they're way better as an early defense unit, and awesome versus carriers ! There is finally a way to beat a carrier fleet without carriers, using mines to ANNIHILATE interceptors before vikings jump in
All : A mine has a 0 targeting priority for our opponent’s units, if unburrowed
TvP : An oracle is killed by a widow mine after having the time to kill 1 or 2 scvs.
TvT : A banshee isn’t killed by a single mine shot ! ! !
Tank : the unit that defines positionnal mech play. Even if we don’t mass them, once we have some, we have to adapt our playstyle to them, playing slower and with careful positioning. In low numbers, they’re a good support units, able to deal some AOE damage to clumped up units like roach, or to snipe banelings. In high numbers, tanks end up flattening everything on the ground
All : unsieged tanks have a really good dps, and can perfectly fight without sieging versus stalkers when both are in a small number, or versus an ultralisk army with some kiting
All : Starcraft 2 tanks have a smart targeting AI, meaning they won’t overkill anything, wasting potential tank shots, even when used with shift+attack
TvZ : Tanks with +1 attack will oneshot zerglings no matter their armor upgrade
Thor : a scary all-around mech unit. They do have a really strong ground to ground attack, two okay-ish ground to air attacks, and a lot of hp. They act as a buffer between both armies, taking a lot of damage/attention while delivering a high amount of damage to everything. They have weaknesses in their buggy AI (extremely slow to target/react, especially when facing both air and ground) and size (makes massing them extremely ineffective)
All : Some thors with a ton of scvs are nearly unkillable in low scale fights. Think about it the next time a zerg tries to roach-drop you (people may remember about the MvP roach drop defense in WoL when he has his 2/4 first thors, by simply pulling 2 bases worth of scv and enjoying the sight of helpless roaches unable to take out these titans)
TvZ : +2 attack makes thors able to two shot mutalisks
TvT : the secondary air attack (high impact payload) makes thors ignore point defense drone, at the loss of the AOE effect and +light damage
Banshee : a high dps, invisible flying unit. Banshees are EXTREMELY STRONG (people may remember that, actually, it was adding banshees to my ghostmech army that made it so strong in WoL)
TvT : when we control the sky, a single banshee won’t hurt (well, it’ll hurt but.. you see what i mean there)
TvP : chain cloak/decloak them to make them less vulnerable to feedback !
TvZ : a banshee beats a queen in a 1 vs 1 situation
Viking : well, i don’t like them.. but we don’t have the choice there. Our other anti air options aren’t reliable (mass thors is terrible due to their speed/size, mines are random/requires to be under his army), so massing vikings is needed to control the air
Raven : ah, the bread and butter of lategame mech, also a really controversial unit , basically the terran’ equivalent to WoL infestor. Lots of utility and usages available, and is usually used massively in the lategame
All : Auto-turrets benefit from building uppgrades
All : Seeker missiles does NOT require vision once the missile is casted !
Battlecruiser : avoid them in most situations, reallyBCs are extremely vulnerable to vipers, raven/viking, and tempest/VR, all of them being the backbone of each race’s lategame versus Mech. However, if we can get a tons of them with the right support units, our army become nearly invincible. October 2014 : i am starting to use these bad boys more & more vP & vZ ; there is just something to remember : NEVER overcommit to them (when the opponent is starting to get counter units, stop producing them !) and NEVER use them without adequate support. Your number of BCs is ALWAYS linked to how much support (usually, viking/raven) you have compared to his counter units.

Ghost :
Energy : will edit after the next patch that’ll put the upgrade back in the game
Cloak : (TvP) we get it once we’re maxed with some ghosts and have some gas to spare ; (TvT) we get it asap when we go ghost lategame
Raven :
Energy : i don’t really use it anymore, it is “cool” to have, but since i tend to be much more conservative with my raven count/energy, it isn’t as useful as in WoL, when ravens wanted 125 energy for the missile ASAP
Spell duration : This is interesting. Even though it can be pretty useless in some situations (like in a really fast-paced game where each fight will take place at a different location), once things start to get a little slower and we can fight in similar locations each time, having them last longer (which also means more energy) is quite strong. A must-have versus Swarm hosts or tempests.
Hell(ion/bat) :
Blue Flame : get it early (between 10 and 15 minutes) in TvZ/TvP if he’s going to heavy zeal/lings or if you go for like 4 thors + hellbats, otherwise delay until max. I often skip it in TvT since marines/hellions are smashed by tanks already.
Hellion/hellbat transformation : don’t worry, the upgrade will be back soon.. with a bunker building time increase as well, of course.
Mine :
Fast burrow : If for some reasons you go mass mines , this is really good to get, obviously
Banshee :
Cloak : with the low cost of the upgrade, getting it if you get more than 2 banshees is extremely useful, increasing their survivability / ability to do damage a lot

- More often that not, the safest option is the best in this style (and almost everything else is a deduction from this)
- Economy : walking on a thin line between greediness and safety is important. You won’t see me going triple CC before factory TvZ, but you won’t see me going for 1-1-1-getting-my-full-tech-tree-up-to-battlecruisers either. You need as much resources ASAP, but you cannot rely on the effectiveness of marines (and the general ability of bio play to kick in quickly once stim/medivacs are out) in the early game. Later in the game; remember that cost effectiveness can make up for a lesser income
- Positioning : When not pushing, your army must be positioned between your opponent, and your most important “macro location”. In the early/midgame it tends to be your 3 first bases, in the lategame, things become a bit more complicated since it’ll be both your production area, and your new mining bases, required you to go forward and take a more forward defensive position
It means that when you push or move, you have to choose between 1) pushing your opponent away from your base and your back, 2) have his army too weak (for whatever reason) to threaten you seriously, can be dealt with by your reproduction / hellions, 3) be in a situation where you can deal with the backstab (starting to pre-siege tanks, stop your whole army to prepare a trap, find a good location that forces him to make a move instead of waiting for you to get caught out of position, etc) / a tradebase (tanks / PF / walls at home, or main army superior in any situation, allowing you to win by lifting and going full tradebase mode.
Also, every single army move should have a goal. Anticipating your opponent’s move, protecting a new base, etc… Don’t move for the pleasure of moving, your army is too slow and requires too much set up for this
When your army arrives in a location it’ll hold for some time, ALWAYS take some actions to get a good formation, some tanks sieged, hellbats at the front, concave, couple of turrets, air army ready to intercept any threat . . . DO NOT LET IT JUST SIT THERE IN A BALL
- Scouting : it should be done often, especially once your opponent reaches 3 bases (allows for a slow air transition, while 4 allows him to go allin on it). Use hellions/banshees/scans, learn to check if what he has on the field (in terms of army, upgrades, infrastructure) is in check with what he should have, and if it isn’t, get worried. If you do not know at all, assuming the worst (air switch) is often the best option.
It is important, especially as the game goes on, to be able to learn to find clues rather than absolute proof of what he's doing. It is VERY important to learn to identify what is "normal" for an opponent to have at each timing in the game, the best placement for hidden technologies, to identify from his army moves if he's trying to hide something through agressivity or denying a specific area of the map...
- Army composition : The midgame is focused on your ground army, with some air support. The longer the game goes, the more “equivalent air + ground army” will become your objective. But since we, opposed to WoL, won’t go for mass BCs anymore, we need to still have some reliable (and seeker missile isn’t exactly reliable) ground power, so going for 80% of air isn’t an option.
Also, remember that playing a tank-based play doesn't mean getting 30 tanks every game. Tanks requires a lot of support.
- THINK : i cannot stress this enough. Mech do not lead the game, mech is all about anticipation or reactions. Your unit composition, your pushes, etc . . . You either chose it beforehand by assuming what is going to happen / try to predict, or do it as a reaction to something that happened in game. There is no inbetween with mech.
- Be Reactive : pushes, army moves, composition shift... they mostly depends of what your opponent is doing. Be ready. Especially about pushes : i don't talk about it much because, in HotS, there is barely any timing pushes for mech. It is all about realizing you have the opportunity and seizing it !
- Be Active : Even when turtling ! Have hellions on the map. Banshees. Keep scanning. Do stuff, but remember the previous rules : do useful stuff. Scout, prepare to intercept his army, try to find any opportunity to punish him, fry workers, etc !

- It is extremely important to study maps in order to learn where / how many turrets must be used : some areas can be covered by our idle air fleet, or by forward bases, etc, while some others can require a double layer of turrets in order to repel this doom drop or mass mutas force
- Once we gain access to triple mules + have our midgame production ready, we start to truly get our turret ring up. Before that, just make turrets at important locations like mineral lines IF NEEDED. After that, add turrets at every exposed areas of your bases, and keep adding them, especially in TvZ where mutas is a threat and a strong muta ball can roll over 8+ turrets
- Sensor towers are our best friends. They’re relatively cheap for what they do, and you should also learn how to place them for each map / position / matchup
- Once we’re maxed, we can start slowly sacrificing scvs if our opponent isn’t trading too much with us, replace them with CC (we won’t sacrifice too much scv if we cannot both replenish our army AND get more CCs - otherwise we’ll run out of minerals quickly)
- Again, 3 bases allows for a bumpy and risky air transition for any race. Learn to identify a standard midgame army size/upgrades/infrastructure, and if you realize there is “not enough stuff”, look for what is going on ! 4 bases means he’ll usually be maxed and is probably getting ready for it without crippling too much his other expenses, so be ready to find it and do the same in time !
- Better safe than sorry. Our army is EXTREMELY expensive and fragile, relies a lot on positioning and control, so always play safe, scout a lot what is going on, and don’t stay blind ! We have hellions, scans, banshees, USE THEM
- Our early marines are good and cheap scouts on big maps. Take these 6 marines, put 1 of them on each expansion site / important paths, enjoy. Even if they can’t tell us all our opponent do, we know that as long as they’re alive, he didn’t took this base or attacked there
- At home, it is better to stay in hellion mode to be ready to defense harass / scout / etc. Out on the map, we should keep most of them in hellbat mode, with a few in hellion mode to protect our flanks.
- When you get two armories, it is good to put one in the main , and one at the natural, so a drop / muta ball / etc won’t be able to snipe both !
- When using seeker missile, don’t put 10 of them on 1 unit. Spread 2-3 seeker missiles on several units, and if he’s really committing (using PDD, blinding cloud , stim . . .) drop a lot of them, but KEEP SPREADING THEM. You don’t want him to dodge 10 missiles by moving 1 unit away
- Obviously, do not do the opposite, do not drop too few missiles on each unit or section of his army to no kill anything and have him run away to heal
- When using seeker missiles, on fast units especially, remember that your opponent can rush towards you. Be ready to fall back !
- When you have enough ravens (8+) to have them becoming your main fighting unit, remember that it is often better to drop some missiles and run away rather than engaging : at some point, missiles will land and you’ll be able to take an easy fight. Even if he's good at dodging... create opportunities. Attack when he's idle / screen away macro'ing. Force him to commit to defend bases. Send a couple of suicide raven for point blank seekers
- Building range uppgrade is basically a +1 attack uppgrade for turrets

There is a lot of builds leading to mech in TvT (gas first banshee or raven are very common, the forgg build is another strong option) but what we’ll mainly study is my own mech opening, my standard since early 2012 :
+ Show Spoiler +

If everything goes perfectly, our units should be :
- Marines (At least 6, but can go as high as needed)
- Tanks (constant production)
- 1 optional hellion
- 1/ 2 viking(s)
- 1 raven
- 1 banshee
We obviously have to adapt. If he’s 1 basing, keep making marines, skip the hellion, if he’s going for a fast marine tank viking push, get double viking production asap, etc...
Our army should be in our base for defense at this point, except maybe a marine / hellion (usually a poor scv, anyway) to scout his position

October 2014 : I do use more and more often variations of hellion/viking openings out of 15 gas, with 5:30-6 min e-bay these days. The converging point is the same anyway, having a 3rd CC & 3 factories + 1 port aroun the 10 minutes mark. Search for example for the ForGGeddon opening ,which is quite close !

We should have our 3rd CC on the way, and a 3 factory (2 techlab 1 reactor)/ 1 port (reactor) soon available. At this point, while starting a 2 tank / 2 hellion / 2 viking production, we do have quite a few options :
- More factories : it is standard for mech to have up to 5 factories on 2 - 3 bases. I don’t personally like it much, preferring adding more air and double upgrades to a 5 fact production. I’ll usually add 1, in order to be safe, but TvT being a matchup where i want to get to the air stage ASAP, i prefer to add a second starport instead of the fifth. (Even though you can and should go to 5 versus really aggressive bio players or if you want to be out of the map yourself with your main army)
Both 1 reactor and 2 reactor for factories can be used, but i do find the 1 reactor 4 Techlab option more versatile, losing one hellion on each production cycle don’t change things insanely, but losing one tank/thor can be kinda sad. Also, i do not rely that much on hellion harass/sacrifice, which might affect me on this decision quite a lot.
- More starports : Especially if we aren’t going to too much factories, another starport can be quite strong to start adding banshees / ravens to gain and abuse air superiority. This is insanely strong versus a mech opponent who is also going for tank/viking play, but didn’t make an early raven like us. However, since air units are quite fragile before we have enough tanks to protect them from the ground, and enough ravens later, adding more than 1 starport too early can be quite dangerous, if our opponent isn’t trying to get to air
- Armor(y/ies) : another choice we have. My own preference is to go for double armories, since it make our mech (and even more, our air) army MUCH stronger. All of our units deals a lot of damage, which are improved a lot by upgrades, and a lot of units we’ll meet will shoot fast/several shots at a time at us, making armor upgrades quite useful. 2 armories + 5 fact + 1 port can be quite hard to sustain (especially when starting 2/2), so it is mainly a matter of preference, depending of how much we want to favor upgrades for later, or a stronger army now, of how much vikings we do produce (personal preference : constant vikings production)
- Fast fourth : not a really common thing from me in HotS, but it is definitely an option, especially if our opponent is a bit too passive and/or tried some kind of stupid move that reset his army while barely scratching ours

At this point, if his tech choice isn’t known yet (look for upgrades on marines, hellion numbers . . . ), we need to burn a scan in his main, look for his production facilities, upgrades buildings, etc. We start to prepare for drop play (fast double marine drop can be quite annoying… and doom drops later) by starting turrets, grabbing our third with a sensor tower to secure the area while positioning our army forward

If he’s going for bio, he’ll drop. Go for a relatively early turret ring (on 3 bases) + sensor tower on our most exposed main’s edge, power on hellbat and tanks, add a 4th factory ASAP (a 5th can be useful if he’s trading a lot), a lot of CCs early (he’ll expand a LOT and we need to be able to at least get some minerals easily with getting as much army supply as possible.. and also to have a lot of scans) and start to slow down viking production at 6-8.Have a couple of hellions patrols taking out marines here and there and threatening him, and pick medivacs with your vikings whenever he’s too close. Once our tanks numbers start to get above 10+, we can start to move out more aggressively on the map, securing a fourth, preparing an air transition and threatening his own main bases cluster (opening us the possibility of sending a couple of units to deny / disturb some of his far bases)... but remember positioning rules ! ! ! Also remember that since he uses a lot amount of gases, he might himself go for an hard air transition early . . . be ready ! Keep your eyes open, follow his army movements, make sure to anticipate and deny any drop / run by attempt, and don’t let him bleed us slowly.

If he’s going for mech, our air superiority should prove worthy quickly. Be wary of some kind of 5 factories bust with thors added (we might need to retreat on 2 bases there, + land vikings), but outside of that, our early raven + banshee should give us air dominance, allowing us to pick up tanks easily. Versus this, going for double starport (ending up with a 3 fact 3 port production ) can be good, but may be dangerous on some open maps where our opponent can take us apart with a couple of big attack forces sieged in key position. It is safe however to go for a 4th factory + 2nd port relatively quickly for some ravens / banshees. We need less orbitals in the midgame, since he’s going to expand less than a bio player, and an air transition is easier to spot without scans (he’ll often retreat entirely to his bases, and his lack of gas units will be easily spotted).

If he’s going for a weird super fast air play, remember that thors RAPES banshees, and BCs without upgrades takes forever to kill turrets / thors. Stay cool, makes some thors / turrets, and transition to viking / raven yourself.

Regardless of his play, adding 1-2 thors for extra safety against banshees (and as a damage buffer for our tanks) is always good. Once the threat of big 2-3 bases busts is over (we have enough tanks) and our infrastructure is done, it is good to restart vikings production (tanks still have the priority of course)

Our fourth is ready, we start to stockpile command centers, to add starports, aiming for a 5 fact 5 port setup . . We have turrets rings + sensor tower on drop paths, and our scv count is starting to get lowered. Keep preparing command centers, and if it is safe, take new bases. We are now producing a lot of ravens, with some tanks / thors / vikings / hellions added depending of his own army

Versus bio armies : our tanks should flatten any bio army at this point… and our ravens, too. Well placed PF + 2-4 tanks can terribly damage a bio army, and as long as we don’t get caught out of position, weshould be able to deal with it easily. Keep an healthy tank numbers (16+) in our main army, get more ravens, cut vikings (10-12 should be enough). We can divide your ground army in two, using one half to rampage his expansions while the other stay between him and our bases, and being ready to reinforce wherever he’s with our air army. Use a lof of scans ! His goal is to catch our armies unprepared, our goal is to force him to charge into us while prepared or to lose economy / production.

Versus mech armies : Keep enough tanks (10+) to make him unable to attack effectively into us, and abuse ravens ! Pdd absorb EVERYTHING he can have, so just use banshees and seeker missiles to chase him away. At some point he has to choose between doing a suicide attack in your ground, getting destroyed by your air, or switching to air himself.

Versus air armies : Now, we dance. The fact is that it becomes all about control and strategy. A few tips :
- Have some “safe zones” with a lot of turrets where you can retreat your air force if things goes wrong. Honestly, 6-8 turrets can change everything
- “missiles and run” is often better than “stay and fight”, especially versus a maxed air army : at some point he’ll commit and you’ll be able to land some missiles. Aim especially at battlecruisers
- DON’T MAKE ANY FUCKING BATTLECRUISERS YOURSELF, except if you totally won air superiority (like, you have 15+ ravens 15+ vikings, and your opponent is going back to ground)
- If he’s committing too heavy to his air, remember : our air army is built to handle a superior air army, and can do so quite easily with good control. We still have tanks on the ground to deny bases
- The addition of 2-6 thors to our army (especially if he skips battlecruisers or if we weren’t able to get a lot of ravens early) is really good to exhaust PDD really fast
Dance with your air army, block his attack attempts, dodge missiles. Meanwhile , use your remaining ground units for counterattack, drive him crazy, and at some point you’ll be able to both destroy his air army and his economy/production.

Overall, winning can be tricky. Lategame TvT tends to be a bit... strange. It is often easy to fight runby and harass, but clashes between armies are extremely violent, scans are spammed, and compositions must be shifted carefully. Winning is a combination of :
- Getting his resources low (force trades / destroy expands with little tank/thor squads or BFH if he makes orbitals)
- Destroying his army (obvious)
- Lowering his production (through economic damage or direct attacks ; versus agressively positionned players, it can be good to send hellions into his bases, convert them into hellbats, and destroy depots / addons / etc.)

There is a lot of possibilities here. My personal favorite is the Flash 1 reaper expand but 12/12 2 reapers, 11/11 3 reapers, CC first, or 1 rax expand are all fine. All of them leads to hellions, followed by banshees.
I’ll assume the Flash opening is used, which is basically :

12 rax 12 gas
Reaper
CC (before second supply)
Reactor
Second supply
Factory
1-2 Marines (Flash goes for two most of the time)
Factory on reactor, Starport, techlab on rax
Hellions (4 before 3rd CC if CC before arm / fact, then 2 after ) / Banshees
3rd CC / 1-2 armory / +2 factories (in any order, with this being the standard one)

Use reaper / hellions / banshees for scout, creep denying, etc . . . nothing out of the standard there. TvZ haven’t changed much about the early game in a looong time.
Be really attentive about the timing / saturation of the third, evolution chambers, number / positioning of queens. Hellion/banshee can defend anything (as long as your hellions don’t get stupidly caught in the middle of the map, and banshees don’t get out runned by roaches because you weren’t in position), but you have to see it coming, and to be ready to get informations about his follow-up (especially if you don’t see anything suspicious before T2 actually) with a scan in the main.

At this point, third landed / landing, hellions / banshees normally chased away from his side of the map. factories 2 and 3 starting a thor. The first important step is to find what he’s doing with his T2 tech (remember the scouting rule !) :
- Mainly zerglings : high risk of mutalisks play, but might be fast SH and / or T3 too (look at zerglings upgrades around 10 minutes !)
- Roaches : Early (6-8 minutes) defensive roaches isn’t always a sign of roach-based mid game. We need to look at their upgrades as with zerglings. The fact is that, since they’ve a critical upgrade (speed), we should quickly (2-3 minutes after lair) know how much he’s dedicating to them. With roaches comes the threat of hydralisks. Get a shitload of tanks, be ready to retreat if you realize you’re outmuscled in open ground, but don’t forget than “low” (20-30) number of roaches can struggle versus 4 thors / 2 tanks / 8 hellbats + some pulled scvs
- Mutalisks : usually spotted by the zerglings-favoured ground, and a common “by default” option. Refer to the “how to deal with mutalisks” question. If, by 9-10 minutes, the zerg hasn't shown any kind of gas tech, it is safe for us to get at least a turret per base around 11 minutes.
- Swarm Hosts : hard to spot, most zergs will kind of “randomly” transition to them after something else. Dealing with them requires a massive amount of tanks (12+) and later in the game, ravens for PDD. We need to start dropping / sending hellions everywhere once we see this, making sure to draw his attention away, winning time for the air transition.
We can go up to 5 factories (still 1 reactor !) there, with your starport either on a techlab (more banshees, earlier ravens - MvP.Wol style, and it is by far my favourite option) or reactor (vikings, better air control versus vipers / mutalisks / broodlords, the favored option currently). Get 2-4 thors early, then power on tanks unless he goes MASS mutalisks. Use hellions to deny some creep, force his armies away (zergs tends to value their creep more than killing blows opportunities on you :D), and get some drones. I’ll in most situations 5 . Scan for his tier 3 every couple of minutes or so, starting at 14 minutes. Consider a relatively early fourth (around 14 minutes) compared to other matchups, and feel safe to cute units relatively early to prepare the lategame transition (orbitals + more starport) once you have enough experience to identify windows where he cannot do anything (for example, after a big roach push with few losses for us, and no T3 : there is few chances he’s going to try the same again without “something else”)

The midgame is pretty simple there in terms of execution, since besides mutalisks, which requires you to go in a specific setup with thors / mass turrets + earlier air transition, most things are answered quickly by “more tanks”. From there it is a race, we have to quickly secure a fourth + prepare the lategame before he’s able to get the whole map and flood us with units until death. Still be careful, don’t be a fool and use hellions / scans to scout our flanks, and be ready to quickly reposition our army versus the faster-moving zerg army.

There is some kind of “midgame T3” play that can be dangerous, the most common being roach(/hydra)/viper bust. Vikings helps a lot there, put them in the front of the army to snipe vipers before they can land clouds, while our tanks and thors MUST be splitted well (no more than 2 tanks / cloud !). Be ready, like with all non-baneling based bust in the midgame, to pull a lot of scv to repair

Have some hellions patrolling the map, getting watchtowers, ready to intercept some drones / lings here and there, and putting a bit of pressure on the zerg. Use one viking to clear expands on the map, so the zerg has to actively scout for them instead of knowing easily how much bases we have or haven’t.
Harassing is always a good thing, use your hellions and banshees to keep containing creep (it is a good way to keep mutalisks from your base.. and abuse them when they're in it !). Hellbats hit like trucks on hatch, destroy expands. Send 2 banshees / 1 raven squad to get tumors. Use vikings to kill any overlords on our side of the map. We can go full MvP, using dropships with tanks and lots of hellbats to attack everywhere, especially versus SH play.

Once we do start to get above 150 supply, with +2 upgrade(s) nearly ready, we can think about pushing. Especially if he isn’t going for many (10+) swarm hosts or some early viper busts (well, mass mutalisks can be a problem too… but less, especially since his ground is probably going to be weak and we can split our army when he dashes in and magic box above our thors, killing as much mutas as possible, while our tanks / hellbats destroy his bases), we want to take at the very least a more aggressive position on the map, securing our fourth position, and if possible, we can push it further. With scans and well positioned hellions, we can pretty safely go at least to the edge of the creep to push it a bit back, and if he isn’t going to things mentioned above (which requires good positioning of our tanks, which is kinda impossible to do well while attacking this on creep), we can think about going towards his bases.

When attacking, don’t forget, we do not want to get flanked / surrounded. Keep track of his army at all time, have hellions scouting your flanks, and be ready to fall back if you realize you cannot push and trade effectively. Better safe than sorry ! Especially at this timing ,where a bad engagement can destroy your whole army quickly ,and you won’t be able to replenish it at this stage of this game . . .

During the late-midgame, we need to add 2 ports with techlab, to get ready for the lategame. We'll get a couple of banshees or vikings first, getting ready to switch towards ravens once the 4th is secured.

The lategame is usually starting when the hive is morphing. Both players are 2-3 minutes away from any tech they want and have the income to get it. We need to start denying the zerg some bases, especially on our side of the map : we split our army accordingly, and start to take a position where we can defend most of our bases easily. This is EXTREMELY important especially since most zergs are going to get swarm hosts at some point, and versus these we NEED to have one solid position, we cannot move to fight every locust wave . . .

Our ideal lategame army will be a mix of tanks (15+), thors (4-6, more than in TvT since their stopping power is great versus ultras, and they help a lot versus mutalisks), vikings (don’t get too much, like above 15, unless he’s committing to mass corruptors play), and ravens (around 16 is a good number) and some hellions to support this. As usual, whenever there is a hole in our opponent play, we need to exploit this, however in TvZ it is easier to expand more and try to increase our raven count than trying to attack directly, unless we can just destroy one base or two and retreat, because a long offensive on creep can prove quite deadly for our army, and a failed attack can be punished easy by mutalisks / SH destroying everything we have at little cost for the zerg.

Abuse the strength of pdd and missiles, spread your units well, get a lot of walls / pfs up, and crawl towards him, one tank at a time !

October 2014 : A little addition i made recently is to use a lot more ghosts in lategame vZ. First of all : Why ?
Simply because ravens lack the "instant nuke" potential they used to have ; the zerg can easily dodge missiles. Also, it is too easy for him to dive in with vipers, losing only 1 or 2 to your focused viking fire, while pulling 6 units away . . .So ghost, using snipe, are a good solution to this.
Second : how many ?
6-8 seems to be a good number.
Third : How to use them ?
Keep track of his viper / infestor pack at all time. Our ghost squad should be positionning between his army and ours. Whenever he tries to approach with his vipers, we cloak a few, go forward (avoid locusts so our tanks don't splash them, and have a few pdd ready behind in case of shit !), and snipe the shit out of every caster in range. If an overseer is there, it is the priority ; after that, the zerg simply cannot kill our ghosts, who can in the meantime get 5+ vipers with good sniping speed.
What is also doable is, whenever a locust wave is dead, dive forward before the next one. TvZ lategame is often all about starvation, and each kill counts ! The point here is that, while his locusts aren't there, his only true defense is often infestor / viper to keep our units "locked" until the next wave.. but ghosts can punish these units easily !

In terms of openings, I do use a mix including :
- Gas first Marine/mine/hellion/medivac aggression : fun to play but sadly most protoss knows how to fight it nowadays
- Reaper expand into 1-1-1 : strong scouting, ability to adapt well, but dies stupidly to some things (fast oracle…) and has a hard time getting a lot of gas quickly to prepare the midgame infrastructure + be safe in the later phase of the early game
- 15 gas expand into 1-1-1 (the LG-IM build) : Less scouting compared to the reaper expand, but safer versus most things. I tend to prefer it with mech , especially since we do very little adaptation with the reaper scout regardless of what we scout. I usually uses a variation with a quick gas after fact, and a slightly delayed starport.
- 13 gas factory expand (often with a quick bunker) : a variation of my WoL opening, but it is not half as good in HotS. You’re forced to go for a mine first, and this + the low marines count + late expand can be quite awkward if your scv scout is denied. But if you’re used to it, and confident in your ability to scv scout, this opening is still a good way to expand earlier than a 1-1-1 opening while still having early gases and tech

The two last are my current favorites these days, with the reaper expand used here and there.

I also heard some people do have some success with fast reactor FE openings (1 marine -> reactor or reactor -> 2 reapers / marines), but i do not really like it

Our first goal there is to end up with a marine/tank defense (with the possibility of mine, especially versus oracle openings), with some starports units (banshee for harass / ground defense, raven for detection, viking for air defense, medivac for support ; which one we make here depends on scouting, and our build, especially gas allocation with the raven and banshee / cloak), an expand, and 4 gas mining.

The second step is to get an armory, and at least a second (possible third) factory, switching to thor/hellbat/banshee production with +1 armor. This army is extremely strong on 2 bases, able to compete with nearly anything the protoss can make on the ground at this stage of the game, allowing us to take our third. One raven, if possible, is also a really good thing to make there in order to get some energy for the midgame !

Use hellions to scout his army / third, while our banshees roam the map in order to pick off pylons, probes, misplaced buildings, etc… Nothing that different from my WoL play there !

At this point (around 12 minutes), our third should be on the way, while we start getting our thor count up and a better position on the map. At 4 thors, we do cut them for now, and want to switch to tank production (with a second techlab’d factory if it wasn’t made yet). If we haven’t, we should also get a raven.

Around the 12-14 minutes mark, a ghost academy should be made, and our barrack should make a techlab and ghosts. We stay on one rax production for long, AND it starts later than in WoL, so we need to be quite careful with these, and to make sure we won’t lose them stupidly ! ! ! ! We also have to possibility to switch the starport on its own reactor to start getting vikings / medivacs
Keep production Ghost/Hellbat/tank/Air while setting up turret rings, sensor towers, and macro CCs with our first spare minerals. At this point, scouting must be heavy, as protoss can extremely quickly get a 4th/5th + going air while holding us back with warp prisms / little armies. The only adaptation in terms of composition is if he tries to go for air, with basically, in the midgame :
- void rays : ravens and vikings. Seeker missiles destroy void rays. Also, if we do have a couple of medivacs, ghosts tanks surprisingly well void rays there. Turrets are also effective at distracting them
- Tempests / carriers : the answer for both is basically the same. Early in the game, these units are expensive, slow to produce, and not that effective in low numbers. As soon as we can identify this transition, what should be done is massing vikings (equal supply should be good, considering we should also have some thors and ghosts to help) and to hit him hard. We want our hellions to be looking for his templars, our mech / ghost army to be pushing him away, while our vikings chase his air and snipe it. Scan constantly to not get caught by storm, and abuse the fact he has a lot of supply in production in his stargates, with a low supply low efficiency air army, and a now inferior ground army
- Phoenix : laugh hard, get some turrets, and prepare for your air transition while carefully noting what he’s going for. His phoenix supply means that if he goes for air, he’ll have to cut either his ground support (enabling counter attacks with your ground, and leaving his templars vulnerable) or his air to ground units (then, just cut your air, go for a bunch of thors, and laugh - it is a same than a zerg panicking and making 50 corruptors to fight your raven/viking army.. forgetting your 80 supply of tanks and thors :p )

We need to be extremely careful with your ghosts : the production starts late, and we stay on 1 rax for a long time (if not all the game) ; This is a reason for which i tend to get cloak quickly after the academy is done.After EMPs, they should be sent back in the tankline (let them in range of the fight though, their dps is good !). Our early raven should mainly use pdd / turrets to help there, missile isn't that effective with only 1 raven, while turret / pdd helps a LOT to delay his ability to do damage on our army, and in the midgame our main goal is to keep these expensive units alive !
We need to be careful with your tanks number too, considering the amount of support units we get, it is important to not go to 15+ tanks like vT/vZ. Around 8 tanks is a good number, unless he's really committing to a ground composition and has no air incoming, while your resources are too tight to go for air ourselves besides our 2 starports addition (see below) ; then it is ok to go to 12-15 tanks, but remember ; we still need our thors/hellbats/ghosts to buffer there, and our air force for synergy !

Around the 15 minutes mark, we should be close to max, with our main protected from drops, and we should add when possible a 4th factory with techlab, and 2 more starports (end goal = 1 reactor 2 techlabs), and more CCs. Obviously, the earlier we do suspect an air switch (small army, lots of unused gas, cybernetic core doing stuff . . .), the earlier we should get these 2 ports in order to go for 4 vikings at a time (or some ravens, if needed)

So at this point, we do have your 4th going on. Our end goal with production is something like 2-3 rax / 5 fact / 5 port but in TvP, due to the need of ghosts in addition to our expensive army, we get what we need, and not what we want, until we do have a strong bank. We have a couple of choices depending of what the protoss is doing :
- Staying on pure ground, aiming towards a massive high tier immortal / archon / colossi / HT army : get more banshees, keep a healthy (12+) hellbats buff, and a second rax for ghosts. A 4th starport and a fusion core can be added, slowly getting an healthy (6+) count of BC (but banshees are also a good option). If we can get a really high (12+) count of BCs without him knowing, winning is extremely easy : just send the air army to destroy everything on his side of the map (beware of templars ! ! !) , while the ground army wait in a defensive position on our side. Dealing with so much BCs without air tech is impossible, and at this point we should have enough ghosts and tanks to literally flatten his ground in seconds
- A mix of ground and air (often tempests ) : versus this, the best thing is to use the "how to deal with tempests switch" question content. We can hit a strong timing, where he had to sacrifice something to get his tempests, while not having enough to really fight us effectively. If we cannot it this timing.. the idea staty the same. We get enough vikings, set up a sick concave, and run into hom
- Mass air : this is where things tend to be interesting. What we're going to see is usually Air + HT + a couple of archons immortals (if he doesn't get ground support for his HT, we need to send our hellions forward every fight, quickly )
Here, we need to get to a strong viking / raven army, with, if possibe (but extremely hard to get in this context, since the strength of protoss air requires us to get so many units) BCs in the end, but often it'll be raven/viking with some thors. We need to get up to 25/30+ vikings versus this, with 15-20+ ravens, and a couple of thors (damage buffer, AOE)/tanks (protection against HT) / ghosts (EMP) on the ground. If we can get our BCs out, things get even better, since we can go for a nearly invincible raven/viking/BC/tank/ghost army, using yamato to annihilate his capital ships while Seeker missile deals damage to everything, with our ghosts / tanks keeping his HT away, and vikings taking out tempests.
An important thing against carriers : DO NOT LET YOUR VIKINGS GO IN AUTOFIRE MODE. They'll often attack interceptors, and they're terrible at that. Target fire.

Here, our composition is going to be similar to the midgame, with thors/hellbats/tanks/ghosts on the ground, supported by banshees/ravens/vikings in the sky, with the possibility of BCs in some games. It is EXTREMELY important in TvP to keep balanced army, especially to keep a healthy buffer of hellbats/thors for these 20 zealots warpin. Compared to other matchups, we cannot really get a 20 tanks / 20 ravens / 20 vikings army that'll deal with everything. We also need to posture quite defensively in this matchup even late in the game, because pushing inside the protoss part of the map with storms / feedback, prisms / warp, and the range of their air army is extremely dangerous, especially since our army requires quite a lot of control / positionning (spread air + ground, siege, EMP, missiles, Pdd, focus fire with tanks and vikings and banshees...) in the first secondes of a fight, it is better to stay defensive on our side of the map, and wait for the protoss with our army ready

All : Where can i found good mech informations ?
+ Show Spoiler +

All : Why such a different advice on battlecruiser ? [End of July 2014 ; not totally valid anymore since i use BCs more, but good to know]
+ Show Spoiler +

TvZ : How to deal with mutalisks ?
+ Show Spoiler +

TvZ : How to deal with mass Swarm Hosts lategame, with static defense, infestors, and vipers ?
+ Show Spoiler +

TvP : How to deal with a sudden Tempest switch ? (Can apply to any air as well)
+ Show Spoiler +

TvP : Why using thors in the midgame instead of going for tanks asap ?
+ Show Spoiler +

The main reason is that nowadays, most bio players are doing some extremely agressive 10-12 minutes drops which are hard to fight using tanks on current maps - fall behind a little bit, and then the bio player will bully you and your low tank number, dropping your natural, rushing in your 3rd, etc.. with hellions, your mobility is wayyyy better and you can fry any dropped bio quickly before going back to the frontline