Graven, The Collector

{x}{u/b}{t}, Discard a card with mana value {x},
return a creature card with equal or lesser
mana value from a graveyard to the battlefield
under your control. Sacrifice this creature at
the beginning of your next end step.
Graven, The Collector gains all abilities
of creatures sacrificed this way.
I'm nothing without you, my lovelies.