I had a similar idea, but I think this works better as a death card.
Also, I think that the card should bring the enemy down to 0/1, but not add antimatter or kill the creature. The idea is to weaken it into uselessness, not to outright kill it or make it heal you. There are other cards for that.
If the creature is already under antimatter, then maybe let this card add further to the negative, but beyond that, I would say no going into the negative.