One, if you negate all cards except for that one... why would it be unegatable?
Cards that negate characters and/or enhancements need to be CBN, at least in the battle phase, because of the chance to create infinite negate loops. Look at Holy of Holies, Golden Calf, Confusion of Mind, Assyria's Tribute, and Covenant with Death. They all have a clause like that.
As for the card itself... Why do we need yet another artifact that mass negates? Negate, in my mind, is no longer a creative ability, since you can practically fill an offense and defense now with negates/interrupt the battle battlewinners, and cards like this would just push even more decks to using all heroes that can't be negated (judges, prophets).
Maybe if it had a usage limit like two turns, or if it had a cost, like you had to discard a card from territory or hand to keep it active, it would be better.
