Mother of Bones

Reverberation {1}{b}{b}{b} (At the beginning of your
upkeep, you may pay this permanent's reverberation
cost. If you don't, sacrifice this permanent.)

At the beginning of your pre-combat main phase,
return target creature from a graveyard to the
battlefield under your control.

When Mother of Bones leaves the battlefield, exile
all creatures put onto the battlefield with it.