Wava, the Split Form

As Wava, the Split Form enters the battlefield, you may exile two creature cards from the graveyard and/or the battlefield. If you do, it enters the battlefield as a copy of one of those cards with a number of additional +1/+1 counters on it equal to the power of the other card.
If Wava, the Split Form dies, put the exiled cards into their owner's graveyard.