Assimilated Demon

Whenever a creature dealt combat damage by Assimilated Demon dies this turn, exile it instead.
Assimilated Demon gets +X/+Y, where X is the
total power of creature cards exiled with
Assimilated Demon, and Y is the total toughness
of creature cards exiled with Assimilated Demon.
At the beginning of your upkeep, you lose life
equal to half Assimilated Demon's power,
rounded down.