Acrid

How to unlock: Acrid is unlocked by defeating it in the Underwater Catacombs, the third stage.

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. Remember 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: 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 and speeds allies up, 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.
 * Epidemic will spread on contact with other mobs, as well as attempt to jump to others close enough on the screen. this can multiply itself and do devestating AOE damage to groups.
 * As a melee class, Acrid will do a lot of up close and personal combat, so making him better suited for this is your best goal. Items such as the Hermit's Scarf, Tough Times, Mysterious Vial and Guardian's Heart will offer excellent survivablity, while offensively you'd want the Tesla Coil, Toxic Worm, Barbed Wire and Thallium to take advantage of being right in the thick of the fight.