Ya'roshh, Thundering-Roar

Flying, This creature gets +1/+1 for each Zombie
in each GY. On your turn, other creatures
become only Zombies (battlefields and GYs ).
{w}{b}{g}{t}: Create a 3/3 Black Zombie
token with wither and firststrike.
{x}{x}{3}{b}{r}: Deal X damage doubled to
each other creature, then put X creatures
onto the battlefield from any graveyards.
{u/b}{t}, sacrifice a creature and discard a card:
Destroy target non-land permanent and
everyone mills 1.