Corruptor

The corruptor is a squid-like zerg flying unit.

Overview
Protoss and terran forces alike deeply fear corruptors. Fortunately for the Swarm's enemies, these giant brain-like creatures, with their snapping beaks and dangling tentacles, are usually found near only the most advanced hive clusters. The corruptor is a genetic marvel that can cover targets in acid, causing them to take additional damage from attacks.

Game Unit
The corruptor attacks air units and aerial structures, including units lifted by Anti-Gravity and even colossi. Corruptors are strong against battlecruisers, phoenixes, and mutalisks, but are weak against vikings, hydralisks and void rays.

Strategies
Corruptors are meant to "outlast" other flying units, since they have a lot of HP and low attack, which is why they are effective against low damage, low armor ones like the mutalisk and phoenix, but isn't as effective against the void ray because it can't kill it before their beam is fully charged (in corresponding numbers, that is), or against vikings due to their high damage, range and the fact that they aren't massive and deal bonus damage to armored units. They also have their use against massive air units due to the bonus damage (and the corruption ability), and particularly effective vs colossi before ground troops move in.