Aura of the Mephers

Whenever you gain control of a creature an opponent owns, you may pay {b}{u}. If you
do, put a 0/1 Colorless Mepher Vessel on
the Battlefield With "{t}, sacrifice this creature: exile target creature you control,
then put a X/3 Black Mepher token
creature on the battlefield, where X is the exiled creature's power.".