The Plane's End

Extinction Hydra enters the battlefield with X
+1/+1 counters on it.
When Extinction Hydra enters the battlefield, it
fights all other creatures. For each creature that
is killed this way, put additional +1/+1 counters
on Extinction Hydra equal to those creatures'
power.
At the beginning of your upkeep, if this creature
has 100 +1/+1 counters on it, you win the game.
If not, you lose the game.