Strange Acid Flask

No one would put acid in a flimsy container that wouldn’t hold it, though. That’s something you’re pretty sure of.
Skill required: Nature
Benefit: Tossing this flask at a point in space seems to cause it to burst, like a carefully timed explosive. You create a 20 ft spread originating from target square within [Close] range, dealing energy damage with the [Acid] descriptor equal to twice your level to all creatures in the spread and inflicting a -4 penalty to the AC of each of those creatures until the end of the [Encounter].