Abyssal Hydra

Trample, Indestructible
Whenever Abyssal Hydra deals combat damage
to a player, that player mills cards equal to the
damage dealt.
At the beginning of your end step, place X
+1/+1 counters on Abyssal Hydra, where X is
the number of creature cards in all graveyards.
"It feasts upon the souls of the fallen, growing e'er
stronger in the darkness."