Gravebound (As this spell resolves, put it into your graveyard instead. If it is put into your graveyard or enters the battlefield, if you didn't cast it, exile it instead.)
As long as Marrow Song is in your graveyard, whenever a creature you control dies, create a black 1/1 Skeleton creature token.
At the beginning of your endstep, if there are seven or more creatures in your graveyard, create Marrow Song Dancer, a legendary 10/10 black Skeleton god creature token with "Other Skeletons and Zombies you control get +2/+2." Exile Marrow Song.
