TvT: Reactive Reactor Reaper Hellion

The recent GSL Super Tournament quarterfinal series between Maru and INnoVation was rated highly. Many appear to misunderstand Maru’s Reapers, Hellions, and Medivac timing build in game 1 and 4. This article explains the thought process behind this dedicated build.

The brilliance of Maru’s build is its metagame implications. Having a good understanding of the existing TvT early game is a prerequisite to appreciate the beauty of Maru’s build. I am going to first lay down the background of the TvT opening metagame. I will then highlight the gap in the specific mirror opening match and explain how Maru’s build exploits that.


There are broadly three main types of TvT openings:

  • One Refinery early expand (gas at either 15 or 16)
  • Double Refinery expand
  • Proxy multiple Barracks

I had written extensively about how these three openings interact with each other in this article. I recommend you to read that before you continue.

In that article, I highlighted that double Refinery expand opening was the standard opening in TvT. The opening gets an early Factory, then pulls Scvs out of the Refinery to expand early. This opening has a good timing with two Reapers and one Hellion to deal early damage against one Refinery early expand openings, and its early access to Hellion is great against proxy Reapers opening.

The opening focuses on getting two Reapers and a Hellion early on. When both players are using this opening, it becomes a battle of Reapers and Hellions. The player with more Reapers and Hellions wins the battle, and the outcome affects whether a player can mine on two bases. Hence, players tried to outnumber the opponent by making more Reapers and Hellions, and they figured out that three Reapers and two Hellions is great at overrunning opponent’s two Reapers and one Hellion. Three Reapers and two Hellions eventually became the standard for the majority of 2019. The dominance of this opening was reflected in my Metagame Build Order entries in 2019 thus far. I first introduced this opening in the January entry, and the metagame was stagnate enough that I wrote it again in the May entry. The other two entries were counter builds against this opening (March and July).

Since everyone was doing the same build with three Reapers and two Hellions, players can no longer attack with these five units. This is because, when both have the same number of units, the defender on top of the ramp would win the battle. Thus, players usually position their units defensively when they know that the opponent is also using the same opening.

If both sides were to position three Reapers and two Hellions defensively, then the production of three Reapers and two Hellions in itself is ineffective. The additional Reaper and Hellion are not useful when both sides do not engage. This led to a shift in metagame to favor one Refinery fast expand opening, as it can take advantage of the passive use of Reapers and Hellions with an economic lead (read this article for a detailed explanation).

This shift in metagame does not mean the double Refinery Reaper expand is done and dusted. The opening is still very popular for the advantages I stated earlier. Then, what happens when both your opponent and you use double Refinery expand opening? Do you simply make three Reapers and two Hellions and use them passively? This leads to question:

How can we take advantage of opponent’s defensive positioning in a mirror opening situation?


The above question assumes you know that your opponent is doing the same opening. This means you have to do a Scv scout. With double Refinery Reaper expand opening, a Scv scout is considered optional. One major reason is that you can deal with proxy Barracks cheese without scouting it early. Unlike using one Refinery Reaper expand opening, having the early Factory means you do not need to scout and build Bunkers against proxy Barracks. While not sending a Scv to scout gives a nice mineral boost, you do not know your opponent’s opening. Hence, players usually poke at the opponent’s natural once they have two Reapers and one Hellion, and they can deduce opponent’s opening based on what they see.

Scouting with the two Reapers and a Hellion was considered the norm for a long period of time. Then, when both players use the same opening, wouldn’t the player who position the two Reapers and one Hellion defensively win the battle when the other attempts to scout? Yes, but it goes back to the fundamental issue that you need to know the opponent is using the same opening to take advantage of that. Conversely, if opponent is using a one Refinery expand opening, you want to be aggressive with the two Reapers and one Hellion. Therefore, in order to make the right tactical decision, players now send a Scv across the map even when they use double Refinery opening.

Reaction to mirror opening

After knowing that the opponent is using the same double Refinery opening, how do players react?

Up until a month ago

We had seen some double Refinery expand mirror opening games in IEM Katowice last month. The players generally have two approaches to the above question:

  • Passive use of three Reapers and two Hellions
  • Transition after two Reapers and one Hellion

I have already explained that the passive use of three Reapers and two Hellions is a response against the aggressive use of the same five units. You can take advantage of this passive approach by cutting the additional Reaper and Hellion and building add-ons earlier (i.e., two Reapers and one Hellion). Since you have fewer or equal number of Reapers and Hellions, you will generally position defensively. See vods below for examples.

Maru’s approach in the above vod foreshadows his thought process for the new build I’m about to discuss. INnoVation positioned his three Reapers and two Hellions defensively on top of the ramp outside his natural, showing a typical approach in the mirror opening match. Maru on the other hand knows that the opponent is very likely to position defensively like INnoVation did, so he took advantage of that and transitioned early. Further, Maru positioned his Hellion in the attack path, so he would know if INnoVation decides to attack with his Reapers and Hellions. Maru would then pull his Hellion back and defend with his units at his natural, while he would at the same time send his two Reapers for a run-by when INnoVation’s units are across the map. The image below illustrates the unit positioning of both players.


This suggests two things:

  • Maru understands the equilibrium of the mirror opening very well.
  • Maru prefers to attack and is finding ways to exploit opponent’s passive positioning.

Maru’s reaction

I break Maru’s build into three blocks using the concept of build order blocks.


14 – Supply Depot
15 – Refinery
16 – Barracks
17 – Refinery
@100% Barracks – Reaper, Orbital Command and Factory
20 – Supply Depot (pull 2 Scvs out of Refinery)


@100% Reaper – Reactor (put 2 Scvs back into Refinery)
@100% Factory – Hellion and Starport
@100% mineral – Supply Depot
@100% Reactor – 2x Reaper
@100% Hellion – Hellion
@100% Supply Depot – Supply Depot
Build Supply Depot accordingly hereafter
@100% Starport – Medivac
@100% Hellion – Hellion
@100% 2x Reaper – 2x Reaper
@400 mineral – Command Centre


@100% Hellion and Medivac – 2x Tech Lab
@100% 2x Reaper – 2x Marine

See below vods and admire Maru’s micro with this build.

I must stress that Maru’s build is a reaction to opponent’s opening. It is not a planned build in those games. As demonstrated in the opening block, he uses a standard double Refinery Reaper expand opening, and one cannot tell what his build is going to be. He sent his Scv across the map at 19 supply, so he could tell what opponent’s opening is before his first Reaper is done. After he scouted that opponent is also doing a double Refinery opening, he decided to go for this build as a reaction.

Instead of constructing the second Reaper that you normally do with this opening, he puts down a Reactor. Intuition suggests this is a bad move, because you handicap yourself by having one fewer Reaper in the initial Reaper-Hellion battle. If you were to make two Marines after the Reactor, that is equivalent to a 15 Refinery Reaper fast expand opening. That means, you have one Reaper, one Hellion, and two Marines at the timing when opponent attacks with two Reapers and one Hellion. You are essentially sacrificing map control by not having the second Reaper, but at the same time you do not have the economic gain that a 15 Refinery Reaper fast expand opening would provide.

The Reactor is an investment to make two pairs of Reapers to hit a later timing. Of course, when the first pair of Reapers (i.e., second and third) are still constructing, you have fewer units than the opponent. Conventional knowledge suggests getting the Reactor makes you vulnerable against opponent’s Reapers and Hellions attack. However, as highlighted earlier, players would position their Reapers and Hellions defensively in a double Refinery opening mirror match. Therefore, you can get away with having fewer Reapers and Hellions than the opponent in this short time frame.

The timing is to attack with five Reapers, three Hellions, and a Medivac. This is a gas intensive build that requires six workers mining gas. Normally, Terran pull two to three Scvs off the Refinery to favor an earlier Command Centre, so Maru put the Scvs back into the Refinery after he scouted opponent’s opening. In fact, mining gas with six workers was the prototype of the double Refinery opening four years ago.

The timing attack hits at 4:00. If the opponent gets three Reapers and two Hellions, s/he would have those five units plus a Cyclone at this time. Conversely, if the opponent transitions earlier by getting only two Reapers and one Hellion, s/he would have those three units,four Marines, and a Cyclone. Five Reapers, three Hellions, and one Medivac would do well against both of these. The rest is down to micro.

This build is not designed to kill the opponent with the attack, even though that is a plausible outcome. The goal is to get ahead economically by killing Scvs. The third block of the build order shows how you can transition to a standard 1-1-1 set up on two bases. You get your Ravens etc.

Metagame implications

People seem to misunderstand Maru’s build, thinking that it is a planned build for the two games. I had argued in this article that the build is a reaction against mirror opening. You can add this build to your double Refinery expand opening framework:

I had already explained the first two. As for against one Refinery expand opening, the third Reaper and the second Hellion are redundant, because they are only produced to outnumber opponent’s Reapers and Hellions in the mirror opening match.

I came across some comments saying this is an old build by TY. They may have mistaken Maru’s build with the Reactor first build. The build order for that build is as followed:

14 – Supply Depot
15 – Refinery
16 – Barracks
17 – Refinery
@100% Barracks – Reactor, Orbital Command and Factory
20 – Supply Depot
@100% Reactor– 2x Reapers
@100% Factory – Hellion and Starport
@100% mineral – Supply Depot
@100% Hellion – Hellion
@100% 2x Reaper – 2x Reaper
@100% Supply Depot – Supply Depot
Build Supply Depot accordingly hereafter
@100% Starport – Medivac
@100% Hellion – Hellion

The timing hits at around 3:30~3:40 with four Reapers, three Hellions, and a Medivac. While both this Reactor first build and Maru’s build aim to overwhelm opponent’s relatively small army, they are derived from very different thought processes. This Reactor first build is a planned build that will be executed regardless of opponent’s opening. Using the vod below as an example, TaeJa put down the Reactor once the Barracks was completed, and he did that without knowing his opponent’s opening (no Scv scout). In contrast, Maru’s build is a dedicated response to take advantage of the passive positioning in the mirror opening match.

I hope this post helps you to appreciate the brilliance behind Maru’s build.

P.S. If you translate and post my articles on other sites, please link them in the comment sections. Thanks.

This article is translated and posted on by 绝迹.

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