Heart of the Swarm: Roach Evolution – Corpser vs Vile
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Both give a nice boost in survivability, but also help with situations where they are not much use.
The choice comes down to if your playing style is lacking when it comes to taking down large groups of enemies or slowing down the damage from a few big enemies.
Since I personally thought it would be harder dealing with the big enemies I went for the Vile Strain to reduce the incoming damage from them.
nonononono. You send in a bunch of spawns as tanks, the AI auto acquires them (since you are only playing vs AI in campaign at this point), and your army is then invincible from there on out as you kill more and more and get more spawns/tanks in an endless cycle till the enemy is dead.
The slowing attacks of the vile roach make it very effective against larger enemy units such as the colossus, thors, siege tanks and archons by making their already slow attacks even slower. With proper micro, vile roaches can also kite zealots easily. They are also useful against ultralisks and hybrids, greatly reducing the threat they pose. However, the slowing effect is somewhat wasted on masses of smaller units, such as marines.
The Vile roach gain +3% hit points, +1% attack speed, +5% armor and +1% Biotic Leech per stack of Biomass. Can stack up to 100 Biomass. Passive: Heal 1% hit points per Biomass. Essence Hoarder: Vile roaches can collect an additional 25 Biomass (summary 125). The Limitless: Vile roaches can collect an additional 100 Biomass (summary 200), but gain +1.5% hit points, +0.5% attack speed, +2.5% armor and +0.5% Biotic Leech per stack of Biomass.
During Kerrigans resurgence, Abathur discovered the vile strain by forcing roaches on the world of Mehlus IV to drink microbe-infested water on the planets surface. The roaches that survived the toxic ingestion adapted to produce acidic saliva which were altered by the byproducts of the microbes. When the vile attacks a target, their acidic saliva will act as a constrictive agent. As newer layers are added with each attack, the old layers harden and tighten thus debilitating the target.