Eve of the Apocalypse: Twilight

I think the cooldown is low because there are several items that allow you to negate the debuff, not sure about the name, but there's an amulet you can buy for 720g that can dispel all of the Defiler's debuffs. [wand of negation/scroll of negation/as well as a whole mess of "cleansing" spe...

I've noticed that when talented and cast on self the shaman's expunge reduces his own mana. Not sure if this was intended but seemed like it shouldn't.