Groy, the Walking Grave

Sacrifice a skeleton: Add {u}, {b}, or {g}.

{3}: Create a 2/1 black skeleton creature token.

{u}{b}{g}{t}: Until end of turn, you may cast any creature in a graveyard with mana value equal to or less than the number of skeletons you control.
Mana of any type can be used to cast them. That creature is a skeleton in addition to its other types.