It's OP because it can instantly kill any targetable creature. That includes flying titans, armagios, and whatever those gravity dragons are called. Sure, it may be hard to get on the field, but that doesn't mean it should get to kill whatever it can. Make it only able to kill things with less hp and then it's good.
That being said, it would be a pretty easy card to counter... reverse time and poof. Then your opponent has a creature they can't play because, as I understand, the only way to get this on your field is by fusion. A gravity/aether deck would probably be pretty good too... immortal oty's eat the slimes, and immortal chargers deal the damage.