Alduin, Dawn Devourer

Flying, Indestructible, Protection from Mortals
Whenever a creature you opponents control
leaves the battlefield, it is exiled instead and
Alduin, Dawn Devourer gains +1/+1 counters
equal to the creature's power
{t}Dragon creatures you control gain +1/+1 for
each +1/+1 counter Alduin, Dawn Devourer has.
{x}{t}: Return dragon creature with X converted
mana cost to the battlefield from your graveyard.