I was asked how to use bio against mech. This article discusses the fundamentals in the bio versus mech match up.
There are different mech styles, and each requires you to play differently. The most common style is Siege Tank heavy and uses Hellbats (with Medivac) and Vikings as support. This post focuses on this common style.
The first step against mech is to know opponent is going for mech. Before Legacy of the Void (LotV), there are certain openings that allow the opponent to make a good guess it is mech. Refinery at 11 Reaper opening and Refinery at 12 Reaper opening in Heart of the Swarm are two good examples. In LotV, however, there is no opening that allows you to make a conclusion that the opponent is likely to use mech. You can easily go for bio or mech with any of the commonly used openings.
Is there any specific build that lets you know it is mech? Not really. The common builds are essentially different variations of the standard 1-1-1 set up, and a 1-1-1 set up is ambiguous in terms of army composition. There are two signs that suggest the opponent is more likely to go for mech than bio. One is continuous Hellion production with the Factory on a Reactor. Players still can go for Reactor Hellions with the intention to go for bio, but they usually would not produce more than six (usually stay at four). Hence, eight is the magic number that suggests the opponent is likely to go for mech. The other telling sign is a Battlecruiser build, as it goes better with mech than bio. On the flip side, it is likely that the opponent is going for bio when a 2-1-1 build is used.
You can more or less confirm it is mech when you see multiple Factories. But it is worth pointing out that there are exceptions. In the vod below, SpeCial got a quick third Command Centre on one Refinery with a 1-1-1 set up. He put down a second Factory before more Barracks for a bio transition. TY once explained this on his stream that this is a specific build for that map, where you only have to defend one ramp to secure three bases. The second Factory allows you to make use the defender advantage on the map.
One common mistake is to have the mindset that you need to kill the mech player before s/he gets a huge unbeatable mech army. It is almost impossible to “just attack” and break a mech opponent. Another relatively similar approach is to out maneuver the opponent with drops, but the trades are often regrettable. It is possible to do a successful doom drop, but it requires forcing mistakes. Making any sort of attack into a mech opponent positioning defensively usually leads to inefficient trade. This makes it even harder to attack again as the mech player has an even better army.
Knowing that you cannot simply attack to gain an advantage, many players would want to out expand the mech opponent. This makes sense, but what do you do with your bio army? A good approach is to deny or delay the fourth base. A mech player needs at least three bases to be efficient with production, and s/he would feel comfortable with four bases. In LotV, we have to acknowledge that it is almost impossible to deny a third base effectively, so the contention point is the fourth base.
While a mech army is strong in securing a location defensively, it is clumsy in taking control of a location that is already occupied by the opponent. The mech player has to slowly leap frog the Siege Tanks forward, and this requires the mech player to commit a sizable immobile force at the contested location. This creates an opportunity for the bio player.
How could a bio player take advantage of this? First, you split up two forces, and neither has to be big enough to take on the mech army. Second, you position one group at the path toward the fourth base. This forces the mech opponent to commit an army that is bigger than your group at the fourth. The opponent still has to slowly leap frog forward or s/he risks the bio player stim-attack into the mech army. Third, you position the other group at the other side of opponent’s territory to prepare for an attack. Once the mech player commits his army to take the fourth base, you can attack with this force. The attack can be a drop or what not, so you have to improvise.
The two vods below show how this is done. Pay attention to the army positioning on the minimap.
You want to mix in Marauders and be light on Siege Tanks. The 5-1-1 convergent point should consist of three Tech Lab Barracks and two Reactor Barracks. Players usually add more Factories in Marine Tank mirror match, but Siege Tanks can hinder the needed mobility for this strategy. Hence, a 8-1-1 with five Tech Lab Barracks and three Reactor Barracks is more suitable than the conventional production set up. It is important to note that Siege Tanks still have a role to play, as you want to have a few to siege up at opponent’s fourth base location. The few Tanks make it difficult for the mech army to advance forward.
Unless you can break the opponent with the above strategy, late game is inevitable. A common late game composition consists of Vikings, Ravens, and Liberators/Battlecruisers. The mech player has an upgrade advantage against the bio player in the late game, and the access to Thor with full upgrade should not be overlooked. However, the bio player has economy advantage. I have seen TY tech straight to air with 3-1-1, but I think it is risky and map dependent.
The last point is to have an active bio force of around three Medivacs of supply to go around attacking vulnerable far end expansions.
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