The Summoning Key

{1}{t}: Target player exiles a creature card from
their graveyard. Put a Aether counter on the Summoning Key.
{x}{t}: Remove {x} Aether counters from the
Summoning Key. Return target creature card
with converted mana cost {x} exiled with the Summoning Key, to the battlefield under your
control. It gains Indestructible until end of turn.
It is a black zombie in addition to it's other types. Shuffle the Summoning Key back into your
library.