Dark Gem

These have a 3% chance to be dropped by any chaotic enemy, 10% for any chaotic MOAB, and always drops 5 each chaotic boss. They can be equipped to a tower. 70% chance to increast its fire rate by 2x for 3 rounds and 30% chacne to decrease its fire rate by 30% for 5 rounds. Can be used to craft stuff.

Crafting
Orb of distilled evil