Netherworld Sentinel

During each player's turn, you may cast a
creature spell from that player's graveyard and
you may pay mana as though it were any color to
cast them. If you do, they enter the battlefield as
white and black Spirits in addition to their other
types and colors.
"Few can gain entry to the Netherworld without
paying the price of death. Those few only get away
with it because they managed to outrun the sentinels."
~ Olaf the Unfortunate