Unholy Grimori Lyncher

Pledge - You sacrifice a creature.
(When the pledge is broken, sacrifice this permanent.)
If the pledge is broken, search your library
for a black card, reveal it, shuffle your library
and put that card on top of it.
Persist (When this creature dies, if it had no -1/-1
counters on it, return it to the battlefield under its
owner’s control with a -1/-1 counter on it.)