So I wrote this a while ago, and maybe I should have posted this back then, since this can serve as a sort of mini-guide for those who wanted to do some of Sea's builds or do some Mech TvPing before HotS came out.

I didn't proofread/revise it, so if I'm saying something weird... I might not have meant what I said! X)
But I thought it would be a bit of a waste if I didn't share it anyways, if there's even one person who ends up enjoying or getting something out of this, that's better than nothing.
Also I just wanted to post something (this is 8999th comment) so that I can post what I want for my 9000th post lol.

Also I'm a fan of both Sea and Naniwa ^^

Liquid`Sea vs Naniwa

After one upping Naniwa in Round 3 of the [IPL5] Losers Bracket with a one base hellion banshee build, Liquid`Sea comfortably enters Set 2 while showing his own unique TvP Mech style on Ohana.

Many are sharing the common opinion that Wings of Liberty is getting figured out or that the metagame is staling. Indeed, we have seen an increasing stability in WoL as players learn how to survive all sorts of timing attacks and all-ins. However, if there's one area that still lacks exploration, it's Mech vs Protoss. With Liquid`Sea's success with Mech in TvP against Code S calibre players such as Genius and Naniwa, it might be worth giving TvP Mech one more hopeful chance.

Old Man Ohana

This map is notable for being able to easily defend three bases as well as its narrow shape, allowing more time for a player to prepare a defense, decreasing the angles at which players can harass from, and making it relatively hard to do drop play without being spotted. Another feature of this map is not one all encompassing Watch Tower but two Xel'Naga Watch Towers around the center (which are out of range of each other), thus encouraging and allowing both players to defend their side of the map. Unlike maps with one Watch Tower in the center like Antiga, you cannot as easily contain and starve your opponent.

While this map has shown decently balanced statistics in the TvP matchup in the TLPD International Database, we must remember that those Terrans didn't use Mech. Whereas a Bio player may find the map's narrow nature to make it difficult to drop a Protoss due to the Protoss's ability to build a couple spotter Observers, a Mech player may find this feature of the map beneficial, as it allows you to defend your bases from Warp Prism harass without building many Turrets and because Mech players don't frequently harass via drops. Furthermore, the cliffs around the Watch Towers along with the Watch Towers' proximity to the high ground fourth provides a strong position for Mech to siege up in. Doing so will allow Mech to establish an aggressive forward position of much greater value than Bio because of the more positional nature of Mech. In this game, Liquid`Sea is able to control this area to great effect.

The Opening

Naniwa and Liquid`Sea start the game without anything really fancy. Liquid`Sea places his Barracks at his natural just to force the scouting Probe to poke around a little longer to be sure Sea isn't going for some kind of proxy play. He builds a marine to deny the Probe of scouting and takes his natural before his second depot. Although not as economical as delaying the first Marine, this is essential as otherwise the Probe would be able to scout Sea's double gas. Sea skips the intial SCV scout. Naniwa opens with a double gas expand into fast Robo, adding on his second and third gateways afterwards. Sea opens up Reactor Hellion into Starport, similar to TvZ Hellion/Banshee builds. Naniwa techs to Colossi and throws down double Forge.

No Looking

Sea does an excellent job of keeping Naniwa in the dark for much of the game. Sea's first scout is at 5:50, when his SCV sees one Zealot and two Sentries, hinting the likeliness that Naniwa is going fast Robo and warning him of potential pressure. Sea responds by making an early Tech Lab on his Barracks to be ready to research Siege Mode. He also keeps his Hellions out on the map, ready to burn Forcefields from Naniwa's Sentries and possibly kill one or two of them, which would significantly weaken any kind of pressure. Meanwhile, Sea scouts the map with his four Hellions and four Marines to kill Pylons. It is somewhat common these days to see Terrans walk four Marines bravely around the map to pick off Pylons, and it is not unheard of for a Terran to make four Hellions for a little map control against Protoss. Sea effectively denies Naniwa of map control without sounding off an alarm that screams “I'm going Mech yo!”

In addition to controlling the ground, Sea builds a Raven to kill Observers, effectively gaining complete map control. (His build also allows the alternative of Cloak Banshees to, instead of killing Observers to deny information, force Protoss to delay scouting by keeping his first couple Observers at home, but the openness of the map and the minimal air space makes that choice unfavorable). Although Naniwa knows there is a Raven, which basically never happens in a TvP game with Bio, he doesn't know that Sea will be building more Factories and going Mech (and not doing some kind of 2 base all-in). This uncertainty gives Sea an enormous advantage because Naniwa lacks the information to make optimal decisions. Trying to scout with more Observers is risky and costly, as it takes away time from building Immortals or Colossi, which are both important units against Mech. Sea takes advantage of the narrow nature of the map, seen usually as a disadvantage to Terran due to the increased difficulty in surprising Protoss with drops, and instead makes it an advantage by easily denying Naniwa of critical information.

Securing the Advantage

As Sea takes a strong foot into the midgame, he constantly pokes with Hellions and an air squad of 1 Raven and a few Vikings and Banshees. Doing so allows him to keep an eye on Naniwa's upgrades, army composition, economic growth, and army movements, while also buying space and time to build up his Tank count.

Home sweet home.

On top of the scouting uses, he trades his Hellions for Probes. Although he may not kill enough Probes to match the plain value of his Hellions, sacrificing six hellions for just a few probes isn't a bad trade – doing so threatens the possibility of losing many Probes, pressuring Naniwa psychologically to play defensive. It can also open up mistakes, allowing Sea to run harass elsewhere and killing many Probes if Naniwa doesn't split up his army well and/or if he doesn't react fast enough. In fact, you can see Sea's air squadron is frequently ready to punish Naniwa if an opening presents itself, while constantly searching for any Pylons hiding on the map.

Line 'em UP!

At home, Sea continues to build an enormous Tank count, preparing to take his fourth.

Pushing the Advantage

As Sea takes his fourth, he checks his pocket expansion for proxy pylons and then proceeds to take that powerful position between Naniwa's Watch Tower and Sea's fourth base. It is important to note he takes his entire army to check for pocket expansions, refusing to risk any sort of chance that his army gets caught while split up.

Rooooll out!

Sea succeeds in holding his fourth, and sieges up at Naniwa's Watch Tower. Sea is granted not only control of the Terran's Watch Tower but also that of the Naniwass, all while defending his fourth base. From this position, you are dangerously close to Naniwas's pocket expansion next to his main. In addition, if Naniwa wishes to attack, there is only one remaining path left for him to take. But with control of the Watch Towers, it is easy to pull back and defend or take a headstart with a base race, because the distance Naniwa has to travel to attack is longer than the distance the Terran must travel to defend it.

Terran abuse! Er... I mean Terrain!

Although Naniwa is still mining out of his bases very healthily, he attacks arguably prematurely, as a large engagement ends slightly in the favor of Sea, as the latter is left with many Tanks while the former only a few Colossi with no support.

He'll be coming around the mountain Naniwa will come!

After both players rebolster their forces, Sea presses onto Naniwa's fourth, knowing that Naniwa will not have healthily charged High Templars in time. Although clumped Tanks is by far more powerful than spreading out your Tanks because your Tanks are hitting at the same time, you can also achieve the same result as long as you engage with your Tanks in an arc around the point where the opponent will attack into. Sea positions his army carefully, leapfrogging to Naniwa's fourth. In the picture below, he sieges his Tanks in two main clumps. This discourages Naniwa from attacking head on into this formation. However, attacking down his ramp from Naniwa's fourth base is not favorable neither, as he would have to attack down a narrow choke. This one siege ensured the army would be able to safely reach and siege Naniwa's fourth.

After a couple last ditch attempts from Naniwa to defeat Sea's stupidly Tank heavy army, he loses his fourth base and Sea pushes down to kill what remains of Naniwa's hopes of advancing to the next round.

“embarassing” ~Naniwa

The Future of Mech

Terran Mech has had a shaky background after WoL's beta, with many believing Mech was not viable. In TvT, Rainbow showed against Clide in the GSL that Mech can win without first gaining a significant advantage. It wasn't until months later that the Mech vs Mech “incident” occurred at MLG, with Mech dominating the match-up. In TvZ, Mech was also rarely seen for a very long time until players like Yoda and MVP revived it in tournaments like MLG and GSL. The reluctant rise of Mech in TvT and TvZ proved that progamers may easily opt for more standard, proven strategies than to risk dabbling in potentially weak ones.

Now, history may repeat itself once again. After Hack destroyed Lure with his Mech and putting up a close 30 minute game with PvT specialist Creator in the TSL4 Qualifiers, Mech had yet to show up again in TvP until now retired Liquid`Sea showed his own take. Although Heart of the Swarm is around the corner and we may never know if Mech in TvP would still work years from now, we're fortunate that Liquid`Sea was kind enough to give all Terrans a treat before taking his leave.