Nagash, Tyrant of the Abyss

When Nagash, Tyrant of the Abyss enters the battlefield, create X 1/1 black Skeleton creature tokens with "This creature enters the battlefield with a hollow emblem attached to it" where X is the number of creatures in all graveyards.
{2}{w}{b}, Sacrifice another creature: Unattach a hollow emblem from another target creature you control.
Hollowing {4}{w}{b}