Sibntei, Infested Hoarder

Cripple 5 (Whenever this creature deals combat damage to another creature, put N -1/-1 counters on that creature.)
Sibntei, Infested Hoarder's toughness is equal to the number of creatures in your graveyard.
Whenever a creature dies, you may exile it instead. If you do, Sibntei, Infested Hoarder gets +1/+1 until end of turn.