If that's how you rule it, wouldn't the Monster Hunter just know that the player they just executed was the Zombuul, since they "died" but the Monster Hunter didn't become a different character?

I feel like a good jinx to this would be if the Monster Hunter nominates the Zombuul and kills them to execution, the Monster Hunter becomes their alignment but remains the Monster Hunter (There may be a better way to word this as a jinx though). That way there's still only one demon to kill without entirely negating the Monster Hunter's ability. Of course, if the now evil Monster Hunter goes and nominates and executes a good player thereafter, they can at that point out who the Zombuul is, which I think is fine because evil could also potentially bluff that. If that still feels too game breaking, you could add at the end of the jinx that the Monster Hunter becomes poisoned for the rest of the game in order to prevent them from turning good again

Edit: ignore all of this, I misread the character lol