i think this is a good card but i think that combined with antimatter it makes entropy very strong. how about not being able to use the ability?
Maybe occasionally attack the owner, then keep cost as is.
That's a clever and fitting drawback. How about a 50% chance that Hypnotist attacks its owner instead of the enemy player? It would also make you have to think twice about casting momentum on it to let it survive a fire/thorn shield or avoid a delay shield. I'd really like to keep the ability-using aspect of the move.
Just for clarification, a hypnotized creature would still attack the opponent on its own turn
as well as its owner when Hypnosis is used. Its ability wouldn't be used up, either- you could use multiple Hypnosises on 1 creature in 1 turn.