Recently, there is a metagame shift in the Terran mirror match up openings. This post discusses how different openings interact with each other, and how that leads us to the current trend.

Background

Reaching an equilibrium

Since the last major balance revamp (Cyclone was reverted to patch 3.8), the TvT opening stage is mainly a battle of Reapers and Hellions. I had discussed in-depth about the negative impact the old Cyclone had on TvT in this article. While the balance change breathes new air to the match up, we saw a different type of stagnation developed.

Double Refinery Reaper expand was the TvT opening until recently. As discussed in this article, there is a soft rock-paper-scissors for the three common TvT openings: proxy Reaper > 15 gas Reaper expand > double Refinery > proxy Reaper. A slight advantage exists when one opening is pitched against another, ceteris paribus. However, players quickly learned that 15 gas Reaper expand and double Refinery expand are in fact even when they are pitched against each other. One main reason is that there is a small window for the double Refinery Reaper expand opening to at least neutralise the economy disadvantage against the 15 gas Reaper expand. The relatively heavy investment in gas allows the double Refinery Reaper expand player to have two Reapers and a Hellion out early. At that time, the 15 gas Reaper expand player has only one or two Reaper (depending on whether a Reactor is placed immediately after the first Reaper). This small hit squad of two Reapers and a Hellion can delay opponent’s expansion and deal notable damage. Game theory suggests players are likely to converge to the same option when players have similar knowledge of the existing options (for reference: Nash Equilibrium). Given that double Refinery Reaper expand is not inferior to the other two mainstream options, the metagame reaches an equilibrium whereby double Refinery Reaper expand is the norm.

Finding an edge

Players attempted to find an edge in the double Refinery Reaper opening mirror match. Given that both players have two Reapers and a Hellion, one cannot simply send this small squad to opponent’s side and expect to come out ahead. As a result, the then new standard was to delay the add-ons and produce more Reapers and Hellions than the opponent. The player with three Reapers and two Hellions would crush the other with just two Reapers and one Hellion. Again, we reached an equilibrium with the three Reapers and two Hellions being the standard.

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).

Current standard

Tactical implication

When both sides have equal number of Reapers and Hellions, the one with high ground advantage wins the battle. That means, players should position themselves defensively with their Reapers and Hellions, as the one who attacks is unlikely to come out ahead due to defender advantage.

I want to shamelessly suggest that the popularity of my Metagame Build Order entries may have contributed to my 75% TvT win rate. I wrote that the three Reapers and two Hellions was a strong timing against the opponent who opened up with the conventional two Reapers and one Hellions. It was true, but apparently many of my opponents did not account for dynamic game of game theory. If you read my articles and adopted the build, do you think others won’t? I know this may sound arrogant, but I merely want to highlight the consequence of common knowledge in game theory (my articles do not have paywall). I experienced something very similar in 2010. I copied a one Barracks expand build taught by Day9 on his channel, and I end up playing against the same build on ladder for more than half of my mirror games for that two weeks. Even my opponents pointed that out and we had a laugh. Anyway, all I had to do was positioning my Reapers and Hellions on top of the ramp near my natural expansion, and then my opponent would attack up with three Reapers and two Hellions. After I cleaned up my opponent’s Reapers and Hellions, I counterattacked with my left over Reapers and Hellions to deal game winning damage. I also used different counter builds to crush this three Reapers and two Hellions opening. Thank you for your contribution to my ladder points.

Step 1: Post a TvT build and sell that it's good.

Step 2: Prepare and use a counter build on ladder.

Step 3: ???

Step 4: Profit. — Max Yu (@Maxyusc) March 21, 2019

The new norm

Players eventually figure out that it is better to position defensively with the three Reapers and two Hellions. That became the new norm.

If both sides were to position three Reapers and two Hellions defensively (and transition to mid game without much early game interaction), then the production of three Reapers and two Hellions in itself is ineffective. As discussed earlier, the purpose of three Reapers and two Hellions is to outnumber opponent’s two Reapers and one Hellion. In other words, the additional Reaper and Hellion are only resource well spent if we engage in an early battle. Since the “current” opening metagame dictates players to position their three Reapers and two Hellions defensively, it is only normal for players to take advantage of this.

Finding a new edge

This then brings us to the latest metagame.

One straightforward reaction is to go back to two Reapers and one Hellion for an earlier transition to mid game production. However, the marginal advantage of a slightly earlier mid game production transition may not be worthy of the risk facing the plausibility that opponent attacks with three Reapers and two Hellions. This is debatable.

Single Refinery Reaper expand is back in the mix now, because it can take advantage of the passive use of Reapers and Hellions. If the player using double Refinery Reaper expand is not going to attack early on, it makes sense to go back to an early expand opening. This is evident in the recent pro games. Below is a list of TvT openings used in the GSL Ro16 group A and B.

*KeeN reacted against cheese, so it is not clear if he planned to expand or tech with the double Refinery Reaper opening.

**Cure took the two Refineries at 16 and 17, and he made a Marine after the first Reaper. A variation of the standard double Refinery Reaper expand opening.

There are twelve single Refinery expand (15 or 16 gas), seven double Refinery expand, and three proxy two Barracks. It is clear that double Refinery Reaper expand is no longer the mainstream opening.

If both players do not attack, taking the Refinery at 15 or 16 does not have notable strategic difference in the early game. Yes, there is a difference in mineral to gas ratio and a minor difference in early unit production, but the discrepancies do not affect decision makings if both sides were to go for standard 1-1-1. However, 16 Refinery is smoother than 15 Refinery in putting down an early third Command Centre before tech-ing up, so 16 Refinery has an edge in the transition stage; see below vods for examples.

Using the 16 Refinery Reaper expand opening

After giving some thoughts about the current metagame, I come to a conclusion that 16 Refinery may become the new equilibrium soon. I wrote an article three years ago about how to react to different openings using 15 Refinery Reaper expand in TvT. I’m just going to quickly go through how you can react with 16 Refinery Reaper expand in the current metagame.

Importantly, you should always do a Scv scout with single Refinery expand openings, as you need to know what opponent’s opening to react accordingly.

Vs. single Reaper expand

As mentioned earlier, you can go for an early third Command Centre more smoothly with a 16 Refinery opening than a 15 Refinery opening. Taking an early third Command Centre is in fact a good reaction against opponent’s single Refinery expand opening. In TvT, single Refinery expand is considered an economical opening (Command Centre first is rare). Since you are also doing an economical opening, you cannot effectively change your build order to do an attack that punishes the opponent. Hence, a good way to get ahead as a reaction to opponent’s economical opening is to be even more economical. I strongly recommend you to read this article, where I discuss the logic behind this.

Vs. proxy Barracks

I had already written an article about how to react against proxy Barracks when you use double Refinery Reaper opening or 15 Refinery Reaper opening. You can apply the same method used by 15 Refinery Reaper opening. And that is to spend the mineral saved for the expansion on Bunkers. In the vod below, FanTaSy even cancelled his Command Centre to build two Bunkers on the high ground.

Vs. double Refinery Reaper

As discussed earlier, the double Refinery Reaper opening has a strong timing with two Reaper and a Hellion against single Refinery expand opening. You can apply the method used by INnoVation in TvP, which I had discussed extensively in this article. When you have scouted opponent’s double Refinery Reaper opening, your Reaper is still in production. Instead of producing a Marine after the Reaper that a 16 Refinery Reaper opening usually does, you can put down a Reactor immediately. Then, you put down a Bunker, and your Reaper can stay in there to defend against the two Reapers and a Hellion.

In the vod below, FanTaSy did just that. He actually went on an autopilot mode and queued a Marine, which he later cancelled to use the reaction I mentioned.

The current maps are big, so aggressive openings like double Refinery are relatively weak to begin with. It is easier to deal with that using an early expand opening now than before. There is indirect evidence from this; when you see double Refinery Reaper expand mirror match, players now only make two Reapers and one Hellion. Like I mentioned earlier, the additional Reaper and Hellion are meant to win the mirror opening match, but now players prefer to transition out of it early. Below is an example.

Thinking ahead

I’m going to plant a seed in your brain now.

Now that you have read this article about how TvT opening evolves, do you think other Terran players you face on ladder read this too? If they do, will they use the 16 Refinery Reaper opening and apply the reactions I discussed? Nash Equilibrium assumed all players have the same knowledge, but StarCraft is more dynamic than that. There are patches and new maps. Player improve and adapt at different speed. How can you take advantage of the existing equilibrium?

If you are interested in Nash Equilibrium and game theory, you can try this mini game on New York Times by Richard Thaler (a Nobel Laureate).

Housekeeping

I know some readers are looking forward to the August entry of Metagame Build Order. There won’t be one this month, because a new patch just kicked it. I will post one next month when more games are available.

Rather than posting nothing, I want to share Dave‘s graphical approach to understanding build orders (see below). The TvP build order is a three Barracks Stim timing, which is something that Blizzard wanted to promote with the recent Stim buff. The TvT build order is one of the double Refinery Reaper expand variations. The TvZ build order is a Hellion and speed Banshee build for mech, which is something I had also discussed two years ago. You can enlarge the below images by clicking them.

There are three new patrons this month! Thank you very much Dave, Kyle, and Jensiii! Your support is extremely important for site. Being completely honest here, I was thinking of not posting more articles this month, as I am very busy recently with five research projects. But having three new patrons really made a difference, as I don’t want to disappoint my supporters. You can check out all the heroes in the Hyperion’s Cantina. Thank you!

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