Rinku, the Charge Unleashed

Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Whenever you or a permanent you control
becomes the target of a spell or ability, put a
charge counter on Rinku.
Remove all charge counters from Rinku: He deals
X damage to any target, where X is the number
of charge counters removed in this way.