Zerg’s Three Phase Tech Switch

There seems to be a pattern that Zerg pick their tech choice in three phases of the game. I will discuss some of the common ones.

Background

Zerg is the best race for tech switch because of the larva system. Tech switch has been a common thing in Wings of Liberty and Heart of the Swarm. For example, Zerg max out with Roach, Hydralisk and Zergling, then trade with the Protoss army. After killing most or all of the Stalkers, Zerg will make around 20 Mutalisks which Protoss do not have an answer for in that short period of time. Tech switch is relatively uncommon in TvZ, because the production is linear and Terran do not have to make production choices. Let say, you play bio, you just keep making Marine, Marauder, Medivac and Widow Mine, and it doesn’t really matter what tech switch Zerg make (maybe except Broodlord). If there is a strong tech switch in TvZ, it is usually when Terran play mech. Zerg trade with either the Thors or Tanks of the Terran, then make the counter units accordingly. Anyway, the point is that in TvZ of Heart of the Swarm, the game is largely Zergling, Baneling and Mutalisk for almost the entire game. The only tech switch is to switch away from early Roach investment if Zerg made Roaches.

In contrast, in Legacy of the Void, there isn’t any outright “best composition” like the Zergling, Baneling and Mutalisk in Heart of the Swarm. At least not yet. Zerg can choose the old school Zergling Baneling and Mutalisk, or Roach and Ravager, or even a mixed of them. The strong late game Ultralisk also gives Zerg the incentive to tech switch later in the game. Therefore, there is a pattern that Zerg tech switch more often in Legacy of the Void against Terran now.

Common transitions

The discussion assumes that Zerg do not intend to do an all-in, but plan to play a macro oriented game in general. The three phases are not strictly categorised in “early-mid-late” game, but there is definitely a chronological relationship in that sense. A simple way to look at it is that the three phases can be broken down into the three times that Zerg commit into a certain unit composition. Also, it is important to note that the three phases may not be that clean cut in terms of how you can differentiate one from the other, because there will be those “0.5 phases”.

1. Zergling – 2. Zergling/Baneling/Mutalisk – 3. Add Ultralisk

This is basically the standard Heart of the Swarm style, so I don’t want to explain much. All Zerg add Ultralisk in the late game now, if they can. You don’t need to drastically change the unit composition just to fit the Ultralisk, so the late game composition is Zergling, Baneling, Mutalisk and Ultralisk

1. Roach/Ravager – 2. Roach/Ravager/Infester – 3. Add Ultralisk

Early Ravager timing is effective, and this makes this composition a popular choice in the early game. However, if Zerg want to be more macro focused, this is a less popular composition as it is harder to transition out in the early and mid game. Therefore, it is relatively convenient to just keep using this composition, and get the same range attack upgrade. The Infester is the Lair tech support that works decently with Roach and Ravager.

Of course, there will always be some Zerglings mixed in. Add Ultralisk in the late game when you can.

1. Zergling/Mutalisk – 2. Roach/Ravager/Mutalisk – 3. Zergling/Baneling/Mutalisk/Ultralisk

This is a popular build now, and it really utilises the three phases of tech switch that I want to discuss in this post.

The two base Lair Mutalisk is getting more popular, and I can find three vods from the SSL qualifiers yesterday (quite a small sample size of games). Two base Mutalisk is by no mean a new thing, but the Roach and Ravager switch after that is something innovative. I will use the third vod (Maru vs. ByuL) to discuss this build, and how ByuL tech switches. The other two are not as “clean”. Unlike the other two, this build does not just add Ultralisk to the phase 2 composition. It switches out of Roach and Ravager for Zergling, Baneling, Mutalisk and Ultralisk.

Two base Mutalisk into Roach and Ravager

I don’t want to write up the three phases for all the common builds and compositions, as the fundamental understanding behind them is quite similar. I picked this because it has a good touch of Legacy of the Void, and the transition from one phase to another is relatively clear cut.

Phase 1

It opens up with Hatchery-Extractor-Pool, and gets speed upgrade. This is the most common opener in Legacy of the Void. It proceeds to tech to Lair on two bases for Mutalisk, and then a third base. The early Lair and Mutalisk are the first big investment of Zerg for this build, and this can be considered the phase 1.

The tactical aim is to pin Terran in base, and also shut down drops.

Phase 2

This is when the interesting choices are made. While the Zerglings and Mutalisks do their stuff, Zerg put down the Roach Warren and two Evolution Chamber. It is normal to put down two Evolution Chamber after Zerg use two base Mutalisk opening, but the upgrade is usually melee focused since the composition is Zergling, Baneling and Mutalisk. However, the popular mid game composition in the match up now is Roach and Ravager, so the upgrade is range attack instead. The air attack upgrade shows that Zerg plan to constantly keep a healthy size of Mutalisks. And of course, Roach speed is compulsory.

The transition from two base Mutalisk to Roach and Ravager in the mid game is actually quite smart in several ways. There is a consensus that Roach and Ravager are very effective in the mid game, because the scaling of army in that time frame. You may have heard casters say Roaches are strong against Terran early on, but their value drops as the mid game kicks in. This shows that certain units are more or less effective in different time frames due to the relative army size and the unit composition of the opponent. Roaches don’t do well against Marine, Marauder and Medivac after Terran have access to the core of the bio composition. The same logic applies here, whereby Roach and Ravager are strong in the mid game time frame. All three vods above show how effective they are against the Terran army.

With that being said, the Roach and Ravager composition has one weakness that Terran always try to exploit, and that is the difficulty to deal with multi-drops. The ideal situation for Terran is to constantly drop at multiple locations before Zerg can gather a big enough Roach and Ravager army that Terran cannot afford not to group every unit to defend. Since Roach and Ravager cannot really shoot up, the advantage may snowball and Terran can win from there. This is why the two base Mutalisk opening is brilliant, because it covers this weakness. The Mutalisks work as support units to shut down drops, while Zerg can gather a big Roach and Ravager army.

Phase 2.5

This is the phase when Zerg want to prepare to move from phase 2 to phase 3. You can tell that Zerg try to trade away the Roach and Ravager as they become less effective because of the scaling I mentioned. Clearly, it is not as simple as just go into a big battle for a trade, and make other types of units. There are preparations in phase 2.5.

The final composition is Zergling, Baneling, Mutalisk and Ultralisk. In order to tech switch to this composition, you need to get the necessary infrastructures and upgrades.

Before you start trading the Roach and Ravager, Zerg need to get the following

Baneling Nest
Baneling speed upgrade
Armor upgrade (level 2 – continue to 3)
Air attack upgrade (level 2 – continue to 3)
Melee attack upgrade (level 1 – continue to 3)
Hive

The one level delay of melee attack upgrade is the trade off for the effective Roach and Ravager mid game army. There will be a time when Zerg will stop making Roach and Ravager, and produce Zergling and Baneling.

Next, find a good opportunity to trade away the Roach and Ravager.

The above two images show ByuL defended with the new Zergling, Baneling and Mutalisk composition, and attack Terran’s base with the left over Roach and Ravager. They actually did quite a good amount of damage and traded very well.

Phase 3

This is when Zerg have fully switched to the Zergling, Baneling, Mutalisk and Ultralisk composition. In the second image above that shows how ByuL traded away the Roach and Ravager, you can see that the Ultralisk armor upgrade had started.

In the game, ByuL still made a few Ravagers here and there to counter the Liberators.

The above image shows how the phase 3 composition looks like. The units tab on the top left (click to enlarge) shows that there were only a few Mutalisks, because ByuL ran some of them across a group of Marines. More interestingly, the Terran composition shows how confused Maru was, and how hard it is for Terran to switch tech. The two Thor were meant for Mutalisks, and the two Ghosts were meant for Ultralisks. But Maru basically made little of everything, and he may even make Tanks based on what he saw.

ByuL made some Infestors later, but it is hard to call that the phase 3 composition. This is because ByuL essentially had access to every tech, and he could make whatever he wanted. In fact, his Infestation Pit was built before the Baneling Nest, but he didn’t make an Infestor until it was really late game.

Conclusion

The three phase tech switch appears to be a persistent pattern in the match up. The simple way to determine the “phases” is to look at the upgrades of Zerg, but it is not easy to do it in game from the Terran perspective. The player does not have the production tab available, and has to manually click on the Zerg units to look at the upgrade. Even when you do that, you can only look at the completed upgrade and not the ones that are upgrading. Nevertheless, it is important to look out for tech switch signs like the units produced and whether Zerg try to trade away some units.

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