Looking at HP swing, it's about a 2/3 turn Antimatter. Having it cost 50%/66% of Antimatter makes it UP, in my opinion.
well spotted, maybe in order to balance it, you could be able to use the target's ability ONCE, for balancing porpuses, like being able to use "devour" from an oty to make it eat one of the opponent's creatures
-it would still make sense, because you are "controlling" your target with hypnosis