Even beyond the GP combo, I think this may have balance issues. The only sources of creature healing that would slay this are Guardian Angel and mutant Heal ability - Holy Light damages Death creatures, so it won't harm this thing. What about making it die whenever its health is positive? That way, things like Blessing and CP would kill it. Another option is to give it 1 HP and make all changes to health reverse - Blessing would grant +3|-3, killing this. But that mucks with Heal ability.
Give it a cost hike and make GP a special exception and it'd be fine - there are other sources of CC, like mutate and rewind and BB/freeze. I wonder if you could just make it immune to status effects? That would negate Gravity Pull, Adrenaline, Momentum, Quintessence... "status effects" wouldn't include poison (which wouldn't matter anyway) and changes to the active ability like Liquid Shadow, which is fine.