Dawn of War and StarCraft

[Eldariel]

But if you mix the two, you get an army that is much more than just the sum of its parts.

One of the advantages of said army composition is the speed of both units; the two are amongst the very fastest units in the game giving you an incredibly mobile army allowing for multi-pronged attacks, good harassment, and especially breaking down bases.

With Zergling damage and the speed of the combination and Ultra tanking, Ultraling armies tear down bases in the matter of seconds and yet, thanks to the inherent strength of the combination, require a real counter; a small garrison won't be enough to hold it off which allows for them to force opponent's army positioning quite a bit by the threat of hitting the base. Though that, of course, is entirely a multiplayer matter.

Devourers are atrocious at shooting down air. What they are good at is making it easier for other units to shoot down air. Once you have 8 Acid Spores on an air unit you have almost doubled the damage it receives from every Hydralisk or Mutalisk shot

The real key here is that Acid Spore adds linear damage increase to all future attacks. Or, it actually reduces target's armor by one. Which is delicious with Mutalisk's attack, which is a triple-hit glaive (each Muta attack hits 3 different targets provided they're close to each other) with each subsequent hit dealing 3rd of the damage of the first hit (Muta damage is 9, so 2nd hit deals 3 and 3rd hit deals 1 normally). Add 8 damage to every one of the glaive hits and the glaive suddenly turns from small annoyance to unit wrecker (so 17, 12, 10).

The other effect of the Spores is that they reduce unit attack speed, making them absolutely lethal to air domination units that rely on attack speed, such as Protoss Corsair (which has an insanely fast speed AoE attack that deals small damage with each individual shot, but gets like 4/second). This makes Devourers an air support unit; they're an efficient counter to many air superiority units and enhance your army. This gives them their niché in Zerg vs. Zerg matches which are defined by large Mutalisk conflicts; otherwise air isn't heavily used against Zerg due to the potency of Scourges but in ZvZ, Mutalisks and opponent's own Scourges make it a fair fight so if you get that far, breaking out Devourer can truly demolish opposing Mutalisk army.