Crovax the Cursed (55) [Stronghold]

Crovax enters with four +1/+1 counters on it. At the beginning of your upkeep, you may sacrifice a creature. If you do, put a +1/+1 counter on Crovax. If you don't, remove a +1/+1 counter from Crovax. {B}: Crovax gains flying until end of turn.