Gas first Reaper opening for Mech


The build that I’m discussing is at least one month old since its first notable match in IEM Toronto between Flash and Taeja. Since then, I have seen INnoVation used it in GSL against Cure, and ForGG also used it against MMA.

I didn’t blog about this because I wanted to wait and see whether this build is going to get picked up by others. As it stands now, it is one of the go-to TvT mech builds.

Build Order

Only the core build order is listed. It does not include reaction and other minor adjustments.

10 – Supply Depot
12 – Refinery
13 – Barracks
@100% Barracks – Orbital Command, Marines and Factory
@100 mineral – Supply Depot
@100% Marine – Reaper
@75 mineral – Refinery
@100% Factory – Hellion (3 production cycle)
@100 gas – Starport
@100% Reaper – Tech Lab on Barracks
24 – Supply Depot
@100% Tech Lab – Reactor on Barracks
@100% Starport – Viking
@100% Viking – Raven (Swap Starport onto Tech Lab)
33 – Supply Depot (Build Supply Depot according hereafter)
@100% Reactor – Swap Factory on it (Continue Hellion production)
@400 mineral – Command Centre, then Factory when able. Next, Engineering Bay and build a Reactor using Barracks.
@100% Raven – Lift Starport away from Tech Lab, then Viking
@100% Factory – Swap the second Factory (without add on) onto the Tech Lab and research Blue Flame (Tank production)
@100% Reactor – Swap Starport on it (a pair of Viking then Medivac production)
100% Command Centre – Orbital Command and Refinery. Then, Armory when able.
Third Command Centre when able

Key convergent point
– 2x Factory (Reactor and Tech Lab)
– 1x Starport (Reactor)
– 2 + 1 Command Centre (3rd is building)
– 1x Armory


This is a defensive Mech opening with a complicated build order. As far as possible I list build order in building sequence instead of timing or supply, because it is easier to remember and is better for adapting to weird interaction.

In general, Mech openings emphasize early aggressive map control with Hellions and Banshees over the opponent, who is often a bio user (watch ForGG vs. MMA for an example). This is because bio cannot fight Hellions early on without the key upgrades. Therefore, it is normal that a Mech player takes initiative in the early game until the bio player moves out after key upgrades have completed. Subsequently, their roles swap over as Mech needs to be defensive to hit a certain supply before it can move out.

This Mech build that we are discussing does not emphasize on taking control aggressively in the early game. It starts with a gas first opening into Reaper and Hellion, which should give the player enough information to react accordingly. Do not get a Reaper right after the Barracks has completed, because you need to invest in an early Factory. Also, since 50 gas is used on a Reaper, the Starport is slightly delayed compared to a standard gas first opening. A Scv scout is not necessary because of the Reaper and Hellion.

The fact that this build goes into Viking and Raven production immediately shows that this is a defensive build. Being a defensive build, it must be able to interact appropriately against the metagame’s standard early timings, for example, Cloak Banshee and Marine Hellion drop. The timing of the first Viking is vital, since it lines up well to match a gas first Banshee. The Viking can intercept the first Banshee and possibly kill it before Cloak is completed. I was impressed when I saw Flash did that against Taeja in game 2.

Flash vs. Taeja (Game 2)

The Raven also appears at the right time to match the Claok research timing. A Raven and one to two Viking can shut down Cloak Banshee effectively. The Barracks is used to build Reactors in order to continue production from the Factory, and this is important. There are other main stream Hellion and Marine drop builds. Since the Factory has been non-stop producing Hellions, the number of Hellions will be equal to opponent’s when the drop happens. However, opponent has additional six to seven Marines and a Medivac. Thus, this Viking must try to intercept and prevent the drop, or at least buy time for the 4th and 5th Hellions (producing with a Reactor). Flash even tried to produce Marines to maximise the number of units he could have when he knew Taeja was trying to do a Hellion Marine drop in game 3. This is a really well thought out build for this metagame.

Flash vs. Taeja (Game 3)

The whole game plan is about anticipating what opponent is going to do, and the unit positioning and composition are in line with this general concept. The Hellions and Reaper are parked in a way that opponent cannot move units to your side without being spotted unless they make a big detour around the map. The Vikings are positioned in such a way that the air space is covered too. Personally, I like the four Vikings and a Raven air defense check point before Medivacs are produced. Two Vikings are produced before the Starport is swapped onto the Reactor, and another a pair is produced after the Reactor is attached. The four Vikings make it almost impossible to speed-boost drop.

I want to point out an interesting thing that Taeja does against Mech. In game 2 against Flash in IEM, he continued to produce Vikings when a bio player would have been producing Medivacs to match the first move out timing. Taeja basically had more Vikings than Flash who was the Mech player. This allows the bio player to surprise the Mech player and kill the Vikings to dominate the air, then hug the Starport with the Vikings to interrupt air unit production. A Mech player does not have Marines to get rid of those Vikings. In game 2, Taeja basically went for a Viking and Stim timing to catch Flash off guard, and it is extremely hard to execute that timing. In game 3, at 8:55 in game time, Taeja flew a Medivac to lure Flash’s Vikings out. Taeja planned to outnumber Flash’s three Viking with his four. Flash’s Vikings and Raven would almost definitely be positioned at where a drop is likely to happen (left side), and they had to move if they want to kill the Medivac on the right. The Raven is slower than the Vikings, so Taeja can snipe Flash’s Vikings before the Raven can provide support. The timing in game 2 and the bait in game 3 show how godly Taeja is in terms of knowing the relative army strength to just one unit difference at a specific time frame, and he also knows how to leverage from that. Top top level play.

Like I have mentioned, the bio player will have the initiative when the key upgrades are completed (usually around 12:00~13:00). It is important that the Mech player has enough to hold from a direct front attack. This build could do it either by a superior Tank count or a Hellbat drop. The choice depends on the add-on the Mech player has on the Factory. Flash only had one Reactor Factory and focused on Tank production in game 3, while INnoVation focused on Hellbats with more Reactor. This is also a reason why I stop listing the build order at the construction of the third Command Centre. If you are a frequent reader of this blog, you should know that I emphasize a lot on convergent points. A lot. No matter of preference, the build should reach the above convergent point I listed.

Personally, I like the Hellbat drop style. It is harder for the opponent to estimate your army strength because opponent is blind about the Hellbats in Medivacs, and this can result in a misjudged engagement as shown in the INnoVation vs. Cure game 1. Further, Hellbat drop during an engagement gives much elasticity to the Mech player. It can help to initiate a battle, which is relatively hard for Mech. Bio cannot just stim in and snipe the unsieged Tanks because it is hard to micro against the Hellbats. The Hellbat drop forces the bio player to move backward and engage again, and hence, the Tanks of Mech can indirectly become more effective. This is likely to be the main stream play style for Mech.

INnoVation vs. Cure (Game 1)


10 thoughts on “Gas first Reaper opening for Mech

  1. Thanks for this article Max great stuff as always :).
    I haven’t watched all the VODs yet will do so later.

    Two tings I’d like your opinion on:
    1) How do you hold the good old 1 base never expand marine tank all in? Get a bunker and then skip the Raven I guess?
    2) Do you go banshee if you play against a fast expand. Or is it ok to do the usual thing? I’m not sure how far you would fall behind if your oponent does a 15 gas fast expad.

    1. 1. The best one base Marine Tank push opening is a Banshee opening in my opinion. This build has answer against Banshee. The subsequent Marine Tank push cannot really do much because of the air control of this build, but it is important to get a Tank up in time to defend though.

      2. 15 gas will have economical advantage over this build. Getting a late Banshee doesn’t really serve as an answer for this build against a 15 gas. Furthermore, you need to know if opponent is doing a defensive or offensive 15 gas. This is more of a metagame build against other gas first build.

      1. ForGG plays a slightly different version of this build when he scouts reaper/15 gas. He cuts hellions and delays the reactor for a faster natural and begins banshee + cloak instead of Viking + raven.

        The banshee is not delayed at all; in fact, the timing is exactly the same as a standard gas first. All that has changed is a lower marine count in favor of a reaper and hellion production.

        I think ForGG’s build solves the problem of going banshee with mech. Standard banshee builds don’t worker scout because gas first is a generally safe build and the resource timings are very crisp. Banshees already use starport production time, so Viking + raven is not an option. As a result, there’s no way to react to another gas first banshee except by going marine + raven or scan + ebay + turret (which heavily delays your own expansion). However, the reaper after marine gives the scouting information just in time to adjust the build. Against gas first, Viking + raven and hellions. Against fast expand, banshee + delayed hellions + fast expansion (by sacrificing marine count, you can afford this very early on).

        It’s become my goto build for TvT. I love the versatility hellions afford me. A while ago, I would crush my gas first banshee every game friends with a fast 3cc into 4 rax build. It was safe against any conventional gas first build that didn’t involve hellions – yes, even tank drop and banshee tank push. Reaper, and then hellions give the scouting information and map control to prevent bullshit metagame builds like that.

        1. You touch on a good point. It’s more of a general switch up against relatively later tech builds (e.g. 15 gas), whereby you can go for offensive options with the Starport.

  2. Is there any chance of incorporating a 13 scout into this build? I used to always do 14 gas marine reaper scv timings, and would usually trade my marine and scv for 2 to 3 marines and maybe a scv.

    1. You can always do a scv scout. The trade off is usually having less mineral. The reason why this build doesn’t do a scv scout is that the trade off is less worthy because you can scout with your Reaper and Hellion later.

      If you do a scv scout, 14 is usually the earliest one unless you’ve specific plan in my mind.

  3. Hey hey, ty for your blog again, nice and interesting job :)

    Yesterday I saw MarineLord, a young french GMwho is blessed with a nice micro skill, and also who loves to taunt, pretending on he was best player Europe TvT, just before easily crushing Dayshi 2-0 in “Underdogs” competition on (best french players)
    He said he has been recently training with ForGG and consor, improving a lot, no need to say he opened with that gas-first-reaper-opening-for-mech, the way you describe in your post.

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