The swarmlord

The swarmlord may activate 2 of it's ability's each turn, and then you can pay {3} for each additional activation.
+1: Create a 4/4 screamer killer creature token with trample.
0: All tyranid creatures you controll get +1 +1 until end of turn.
-2:Deal 4 damage divided as you chose among up to 2 targets.
-15: You win the game