Gastly Mist

When Gastly Mist enters the battlefield, search
your library for a card named mistwalker, and
put it onto the battlefield tapped. Then shuffle.
At the beginning of your upkeep put a -1/-1
counter on every creature without shadow.
Whenever a creature with a -1/-1 counter on
it leaves play, exile that creature instead. Put
a 1/1 black spirit creature token with shadow
under your controll.