Universal Cleansing

Whenever a nontoken creature would kill a creature, put a sin counter on it.
Whenever a non demon creature with a sin counter would die, exile it and create a 4/4 black Demon creature token with flying
Whenever a creature without a sin counter would die, return it to the battlefield under its owners control and create a 4/4 white Angel Creature token with flying and "when this creature would die, destroy all creatures with sin counters on it"