Metamorphosis
Ultimate Spell — Buff • Cost: 6
Sacrifice all units you control.
Your non-Demon heroes level to max and become Demons. Put two +1/+1 runes on each, they get readiness, and are invisible until they leave play.
Black • Demonology Ultimate Magic
Card-Specific Rulings
Heroes generally don't have types, so your Demonology hero is NOT a Demon until Metamorphosis makes her a Demon. Once she is a Demon, playing a second Metamorphosis will not affect her. If she leaves play, she stops being a Demon. — Sirlin, 03/02/16
Whenever a hero leaves play, it always loses all properties such as levels, damage on it, +1/+1 runes on it, etc. So it also loses all buffs it got from Metamorphosis. — Sirlin, 03/02/16