Once the early game shenanigans are out of the way, most Terrans currently favor an MMM+siege composition through the mid-game and endgame in ZvT. While it is possible to combat this with muta/ling/bling, most Zergs will attest to this feeling like an uphill battle at times. Even with superior forces and better macro, your army’s inherent fragility and reliance on excellent timing means it can feel like you’re on the edge of a precipice. I believe this is not because of any severe imbalance, but rather because the roach is currently underused. A recent resurgence of roach-based compositions at the top level, and my own experiences on the ladder have led me to believe that a ling/bling/roach composition provides a more stable platform for ZvT.
Why roaches aren’t widely popular in ZvT
While the roach is a staple unit in ZvP and ZvZ, anyone who has tried massing roaches against Terran knows how quickly they get melted by MMM. In early game, roaches are effective against marines, hellions, and reapers. But marauders decimate them, and once medivacs arrive, roach DPS is no longer sufficient to handle any bio composition. The roach has thus been largely relegated to roach rushes and countering mech-only terrans, with the occasional abortive venture into hydra/roach. In fact it is not uncommon for high level Zergs to now play an entire game without dropping a roach warren.
Why roaches deserve a second look
The inherent fragility of muta/ling/bling can be understood in terms of 3 key factors:
(1) High mobility but low life totals: While this composition is excellent in harassing and securing map control, it can very quickly evaporate.
(2) Poor speed synergy: This is a concept I’ve written about previously: http://www.teamliquid.net/forum/viewmessage.php?topic_id=182807 Because the various elements of the Zerg army have disparate speeds, it becomes extremely important to properly time engagements. A very small error in timing can result in the loss of the whole army.
(3) Vulnerability to area of effect damage: All elements of the muta/ling/bling army have a tendency to clump, and are thus particularly vulnerable to splash from thors, hellions, and siege tanks.
The inclusion of roaches addresses each of these issues:
(1) The inclusion of a tanking unit greatly boosts the durability of the Zerg army, meaning less larvae need to be spent after each battle.
(2) Because roaches move at nearly the same speed as banelings, their inclusion improves army coordination and movement.
Upgraded unit speeds, on and off creep.
(3) Due to their speed synergy with banelings and much larger size, roaches uncluster banelings, resulting in less vulnerability to splash damage. The Terran is now forced to target siege tank fire, and even then it is less effective.
In this respect, the roach plays a similar role in the Zerg army as the Ultralisk does in late game compositions, e.g., http://www.teamliquid.net/forum/viewmessage.php?topic_id=187434
In addition, the roach's ranged attack provides an excellent synergy with the melee attacks of zerglings and banelings. As the zergling ball starts to become too large, diminishing returns set in due to surface area limitations. The inclusion of roaches allows more total DPS to be delivered. Note that this is by no means a new composition (e.g., http://www.teamliquid.net/forum/viewmessage.php?topic_id=122427), but I believe it is currently underutilized.
Aiming for the ideal mid-game composition
In the ZvT mid-game, I would argue that there are 7 primary Terran units (Marine, Marauder, Hellion, Tank, Thor, Medivac, Banshee), and 5 primary Zerg units (Zergling, Baneling, Roach, Mutalisk, Infestor). The inherent flexibility of Terran in this match-up can leave Zerg struggling, especially now Terrans are becoming better at using mixed compositions. The arrival of Tier 3 provides Zerg with some additional options, but getting there in one piece can be problematic.
To my eyes, many Zerg players unfortunately restrict themselves unnecessarily to a muta/ling/bling composition when the addition of roaches (and infestors) could be extremely effective. Even at the top level, Zerg players often spurn adding a few roaches to their army as the Terran siege tank count grows, and it’s in these cases that the advantage built by Zerg across the course of the game can start to feel extremely fragile. I would argue that roach/ling/bling is a much more reliable base ground composition, and one that makes good use of Zerg’s general tendency to accumulate excess minerals.
Of course roaches should not be built blindly either; it is important that Zerg responds appropriately to the Terran composition. As a very approximate conceptual guide, I have included a unit wheel below. The idea being that this set of 5 Zerg units acts as a basic palette for constructing the Zerg army, with each particular unit being under- or overemphasized in reaction to what the Terran is doing. For example, if Terran is going particularly heavy on the mech and light on marines, more roaches and less banelings should be built. Of course it is impossible to cover every eventuality with such a simple visualization (e.g., mutas obviously also perform very well against a hellion/marauder composition, and neural parasite can make infestors an effective counter to mass thor). Nonetheless, I believe thinking about this match-up in big picture terms provides a useful framework for developing appropriate responses. For an excellent guide on the Zerg mid-game see http://www.teamliquid.net/forum/viewmessage.php?topic_id=176625
The 5 primary Zerg units and 7 primary Terran units in the ZvT mid-game.
Use of mutalisks
The addition of a roaming group of mutas can complement the roach/ling/bling ground composition extremely well, especially once Terran builds medivacs. The mutas provide a means of shutting down any drops, and provide additional DPS to marines on the run from banelings. They can also be used for standard base harassment, and as I’ve learned from my own games, if Terran responds to this by simply moving out with a marine/marauder/tank composition, the roach/ling/bling composition is much better at holding the fort than ling/bling alone.
Note that there are many possible paths to a mid-game roach/ling/bling+muta composition. Depending on Terran’s strategy, Zerg can potentially transition to this mid-game from a 2-base mutalisk opening, a roach defense to hellions, or a ling/bling response to traditional bio. In my experience, aiming to incorporate roaches from the beginning (and thus broadening your available tech) gives much greater flexibility in holding off the multitude of available Terran all-ins.
Engaging Terran head on
One of the chief advantages of the roach/ling/bling composition is the ability to take Terran armies head on. Typically in ZvT, even once Zerg has achieved a significant advantage, it is a mistake to attack into the Terran fortifications, since it provides Terran with an excellent opportunity to get back in the game. Zerg is thus usually forced to play a game of harassment and starvation. In these circumstances, Terran will continue to turtle, hoping to gain a second wind with a highly cost-effective maxed army. However, with roaches tanking damage, Zerg can actually break heavily sieged positions. For example, see the images below (taken from TSL_Fruitdealer vs. ST_Virus below). Notice that Fruitdealer sends the roaches just in front of the rest of his army to tank the first few siege blasts.
TSL_Fruitdealer attacks into the fortified position of ST_Virus
Use of roach/ling/bling at the top level and replays
Looking back to GSL1, Fruitdealer seemed to be one of the first to make use of this composition at the top level. At the time I was impressed by the fact that he seemed to be playing Zerg in a way nobody else was. His armies were this incredible swarming mass of zerglings, roaches, banelings, and infestors (and even ultras in late game).
http://www.gomtv.net/2010gslopens1/vod/1148 (The whole match is great, but see Set 1 for an example)
Fruitdealer vs. HopeTorture in the first GSL Final
Despite his success, this composition didn’t seem to catch on with many other players in ZvT, with most preferring muta/ling/bling. Since that time, Terrans have gotten progressively better at handling muta/ling/bling, and more recently, other top level Zergs (including IMNestea, CheckPrime, and IMLosira) have started to incorporate roaches into their ling/bling mix with great success. Here are some vods from the latest GSL season.
CheckPrime vs. PoltPrime
http://www.gomtv.net/2011gslsponsors2/vod/61495 (M5 Set 1 for those of you with a season pass)
IMLosira vs. ST_August
http://www.gomtv.net/2011gslsponsors2/vod/61938 (Sets 1 and 2 are both good examples)
CheckPrime vs. oGsNaDa
http://www.gomtv.net/2011gslsponsors2/vod/62034 (Set 1)
IMLosira vs. oGsSuperNova
http://www.gomtv.net/2011gslsponsors2/vod/62599 (Whole match)
TSL_Fruitdealer vs. ST_Virus
http://www.gomtv.net/2011gslsponsors2/vod/62859 (Set 2)
Specific build timings and triggers
The relative timings for roach warren, baneling nest, evo chamber, lair tech, and spire depend entirely on Terran’s play. This means it's imperative to be scouting the front and having a sacrificial overlord ready. A good Terran will try to deny scouting opportunities, but crucial things to look for are:
(A) Is Terran getting a refinery, or opening with two barracks? If it’s the latter, any tech is delayed, meaning your biggest concern is marines. In this case, the baneling nest should usually go down first.
(B) Is Terran expanding? If so, that’s less minerals on marines in the short term, meaning you can drone harder, potentially delay the baneling nest, and get lair tech earlier.
(C) Is Terran building an early factory? If so, you want to respond with a roach warren. If reactored hellions are on the way, you want a spine by your ramp as soon as possible, and a queen blocking the ramp until roaches are ready.
(D) If there’s an early factory, is Terran going banshees? If so, you may want an extra queen, and earlier timing on the evolution chamber. If it’s two port banshee, teching to lair earlier is a good idea, since the long term solution is going to be mutalisks.
(E) Is Terran researching stim? If so, you want to be thinking about lair tech for baneling speed.
Here is a high level example (taken from CheckPrime vs. PoltPrime above).
Terran opens with a single barracks, refinery, OC, into reactored factory and hellions, while building a new command center. He then transitions into tech labs on barracks (researching stim) and factory (researching siege mode), while building 3 new barracks (2 reactors / 2 tech labs on the 4 barracks). He moves out for a timing push as stim finishes, just after the 9 minute mark. At this point, siege mode is nearly finished, and terran has 2 siege tanks, 3 hellions, 6 marauders, and 18 marines:
This is a scary push, and I’m sure a lot of Zergs have experienced dying to something like this. CheckPrime engages with a roach/ling/bling army (5 banelings, about 20 zerglings, 4 roaches, 1 queen) and is able to clean up very effectively with reinforcing lings. The roaches tank for the banelings, while the banelings force the bio back allowing the roaches to target down the tanks.
So how did CheckPrime achieve this? Here is his full build from the vod:
+ Show Spoiler +
15 Hatchery
16 Spawning Pool
17 Extractor
18 Overlord
18 2 x Queen
22 Zerglings
23 Drone
24 Roach Warren
23 Drone
24 Overlord
24 Zergling Speed
24 Drone
25 Drone
Inject / Tumor
26 5 x Drones
Check pokes and sees Hellions
2 x Roaches, and blocks ramp with Queens
Overlord
Check sees Command Center with Overlord, prompting him to drone and start a Lair and 2nd extractor just after the 6:00 mark. He gets a couple more roaches and spine crawler for defense while continuing to drone. He pokes with an overlord to see Terran building 3 Barracks at the 7:00 mark. This prompts him to build an Evolution Chamber, start Roach Speed, then get a Baneling Nest, and start Melee Attack. From here, he takes a third, and most larvae go into ling/bling and overlord production. He actually manages to squeeze out 5 more drones, a queen, and start baneling speed and a spire before the attack hits. This leaves him in a commanding position and ready to pump out a round of mutas after the attack is repulsed. For mortals, those 5 drones could have been roaches or lings, in which case he would have held very comfortably.
16 Spawning Pool
17 Extractor
18 Overlord
18 2 x Queen
22 Zerglings
23 Drone
24 Roach Warren
23 Drone
24 Overlord
24 Zergling Speed
24 Drone
25 Drone
Inject / Tumor
26 5 x Drones
Check pokes and sees Hellions
2 x Roaches, and blocks ramp with Queens
Overlord
Check sees Command Center with Overlord, prompting him to drone and start a Lair and 2nd extractor just after the 6:00 mark. He gets a couple more roaches and spine crawler for defense while continuing to drone. He pokes with an overlord to see Terran building 3 Barracks at the 7:00 mark. This prompts him to build an Evolution Chamber, start Roach Speed, then get a Baneling Nest, and start Melee Attack. From here, he takes a third, and most larvae go into ling/bling and overlord production. He actually manages to squeeze out 5 more drones, a queen, and start baneling speed and a spire before the attack hits. This leaves him in a commanding position and ready to pump out a round of mutas after the attack is repulsed. For mortals, those 5 drones could have been roaches or lings, in which case he would have held very comfortably.
Conclusions
Roach/ling/bling is a rapidly rising style in ZvT at the top level that is proving to be highly effective against mixed bio/mech compositions. The inclusion of even a relatively small number of roaches adds great robustness to ling/bling, reducing the inherent fragility of the Zerg ground army, and allowing Zerg to tackle Terran head on. The style can also be readily adapted to incorporate mutalisks.