Ravenous Penumbra

Enchant creature
At the beginning of your end step, create a
token that's a copy of Ravenous Penumbra
attached to enchanted creature. Then if there are
X or more Auras named Ravenous Penumbra
attached to that creature, where X is its mana
value, that creature's controller sacrifices it and
you create an X/X black Shade creature token.