Acrid

How to unlock: Acrid is unlocked by defeating it in the Underwater Catacombs, 3rd stage. On the topmost land layer, above the water, there is chance for a box to spawn on the rightmost side. Opening the box will spawn Acrid.

Acrid deals huge amount of damage after stacking poisons from his Festering Wounds, Caustic Sludge, and Epidemic. Try to stun targets inside your Caustic Sludge for maximum damage. Remeber that you can fight at melee and range!

In the ending cutscene, the acrid-specific text says: "And so it left, with a new hunger: the hunger to be left alone."

Tactics

 * The poison applied in Festering Wounds is stackable.
 * CAUSTIC SLUDGE has a 17 second cooldown, but the trail itself will last for nearly 15 seconds, meaning that by the time it dissipates, Acrid will be ready to spread another trail shortly. Spam it as often as possible, as it slows enemies down, making it great not only for combat, but for escaping as well.
 * Try to spread CAUSTIC SLUDGE in as wide an area as possible, avoiding bumpy, uneven terrain as much as possible.