Grim, Hydra of the Endless

Reach, fear
Grim, Hydra of the Endless's power/toughness
is equal to the number of hydra heads on the battlefield. When Grim, Hydra of the Endless
enters the battlefield create X 1/1 green and black
hydra heads equal to the amount of mana spent to
cast this creature. Sacrifice X number of hydra
heads, return target creature from your graveyard
with converted mana cost equal to the amount of sacrificed hydra heads, this can only be done
once per turn