Akruvel, the Harbinger

Flying, Indestructible
When this card is cast exile it with X doom counters. At the beginning of your upkeep exile 1 permanent for each doom counter on this card, then remove a doom counter from this card. When there are no doom counters on this card it enters the battlefield with a +1/+1 counter for each card exiled this way. If you can not exile the required number of permanents, you lose the game.