I have been thinking a lot about Reaper opening in TvZ recently. It is a more common opening than 14CC in the current metagame. Players seem to have different preference for the follow up build order after a Reaper opening. I will discuss some of the variations.

This post may require you to have basic understanding of a 12/12 Reaper opening in TvZ.

The above flow chart basically sums up what Terran do in a standard macro game in TvZ. The focus of this post is the transition from 12/12 Reaper opening to the first convergent point. There are several ways for this transition, and each of these has its pros and cons. Before I go into the details, let’s start with a basic build order for 12/12 Reaper opening that everyone is familiar with,

10 – Supply Depot
12 – Barracks
12 – Refinery
15 – Orbital Command and Reaper

In order to reach the next convergent point, you need to add (in no specific order),

1x Supply Depot
1x Command Centre
1x Factory
1x Reactor (on Barracks)

There are three main ways to add these structures. The build orders below are continuations of the above basic build order.

1. 2x Reapers before Reactor

16 – Supply Depot
@400 mineral – Command Centre
@100% first Reaper – second Reaper
@100% second Reaper – Factory and Reactor on Barracks

This is the prototype of a 12/12 Reaper expand in TvZ (also used in TvT mech). The two Reapers can deal some damage if the Zerg player does not handle it well. If both players are equally matched, the Zerg player is forced to make Zerglings to neutralise the Reapers. It is a trade that is slightly beneficial to Terran. However, Zerg can react by sending two Zerglings to Terran’s natural to kill the Scv that is building the Command Centre. Terran will not have any units to prevent the Zerglings from delaying the Command Centre. Thus, the two Reapers are forced to move back to the natural in order for the Command Centre to complete. This counter attack can delay on the Command Centre and force the Reapers away. It is considered to be a good trade to Zerg.

Terran react to such counter attack by positioning the second Reaper at the natural to anticipate the Zerglings. This adaptation then became the metagame for Reaper opening for a long period of time. Knowing that the Zerglings will not achieve anything at opponent’s natural, Zerg player no longer send Zerglings across the map. This results in the second Reaper positioned at the natural in case the Zerglings counter attack. For a while, this has been considered a standard scenario, which shapes up to a 50-50 guessing game for a small opening advantage.

Terran: Should I send my second Reaper over? Will Zerglings counter attack?
Zerg: Is he going to keep his second Reaper at the natural?

Apart from the 50-50 game, Terran has one weakness at this time frame: nothing shoots up. Zerg players simply park an Overlord in Terran base without any worry that they will loss it. This is a huge advantage to Zerg, because that is a key moment for Terran to decide the build order (refer to the flow chart).

– Command Centre (Drone up)
– Starport without Tech Lab: Viking (Move Overlords)
– Starport with Tech Lab: Banshee (Spore), 2nd Refinery = Cloak
– Armory: Hellbat (Spore + Spine)
– Second Factory: Blue Flame (Wall off + Spine)

Zerg have close to perfect information, and that is extremely disadvantageous to Terran. Later, Terran adapted to this according, and this leads to the second type of transition.

2. Marine + Reaper

@400 mineral – Command Centre
@100% Reaper – Reactor
@100 mineral – Supply Depot
@100 gas – Factory
@100% Reactor – Marine + Reaper

The Reactor is down right after the first Reaper. This allows the Command Centre to be built before the Supply Depot. You will not get supply block because the Barrack is not producing when the Reactor is building. If Zerg does not send Zerglings over, this is better than having the second Reaper at the natural because the Command Centre is down earlier. If Zerglings try to delay the Command Centre, you have no choice but to send the first Reaper back. However, the Command Centre is earlier than the prototype, and hence, the risk/profit is slightly better.

The Hellion production is not delayed as the time to swap the Factory onto the Reactor is the same. Reaper-Reaper-Reactor has the same build time as Reaper-Reactor-Reaper. The Marine production is what really makes this transition more superior than the one above. A Marine takes 25 second to build, while a Reaper takes 45 second. The Marine can start hunting the Overlord in base before the Factory completes (almost same time as the Reaper finishes). Although the Overlord can escape, it cannot tell the build that Terran is doing. Terran will only show the build order path when the Factory completes (the third Command Centre can start slightly earlier before the Factory completes). With the Overlord out of base when the Factory completes, Zerg will not have the luxury of close to perfect information they normal do against the prototype Reaper opening. Polt did this in almost every TvZ game in 2013 WCS Season 3.

Personally, I do not like the delay on the second Reaper. Reaper is a unit that losses its value as the game gets longer. Furthermore, that second Reaper appears at the time when Zergling speed is completed. That is, the second Reaper simply joins up with the first Reaper in base to wait for Hellions before they can move out on the map. More importantly, the second Reaper does not add much value to the group of Hellions that roam around the map. In my opinion, it is just not worthy to get a second Reaper after the Reactor in standard play. With this in mind, now compare the first and second type of transition. Get an earlier second Reaper vs. Obstruct Overlord scouting.

After playing some games with both transitions, I concluded that it is best to get two Marines from the Reactor.

3. Marine + Marine

@400 mineral – Command Centre
@100% Reaper – Reactor
@100 mineral – Supply Depot
@100 gas – Factory
@100% Reactor – Marine + Marine

In my opinion, this is the best transition. It has the benefit of the second transition: earlier Command Centre and obstruct scouting. In fact, it does not only obstruct scouting, the two Marines can gun down the Overlord. This is something that the single Marine cannot do. Killing an Overlord this early does not only supply block the opponent, Zerg cannot sacrifice the Overlord later to scout again. The trade off for the Marines is the second Reaper. However, like I mentioned earlier, if you want to get the second Reaper, you should to get it before the Reactor to get the value out of it. Another words, use the Prototype instead. I believe that the rationale behind the second Reaper after the Reactor is due to the “build order fixedness” of the prototype Reaper expand. You simply want to make the second Reaper, because “it feels right”.

I must say I am excited to see Progamers share the same thought. Players like TaeJa, MMA and Ryung were doing this Marine + Marine transition recently. Watch TaeJa vs. Hyun in Home Story Cup and Ryung vs. Symbol in GSTL.

All in all, I believe Marine + Marine is the best of the three transitions. Let me know what you think in the comment below, and I will definitely like to know if there is other transition.