I already answered the sensing bit (answer is yes for anyone else lurking) so as for the second-
Well obviously the success or failure of trying to reverse the spell would be up to whoever's character you're trying it on, so assuming you have their permission first:
The magic that's holding the spell together is primarily the Life Force, which is a level above Billy's (who's already kinda godmode), so it's... pretty ridiculously powerful. However, the fact that it's spread across the village, and Billy is inexperienced, PLUS the barrier makes it weaker than usual, means it isn't what it would be in canon. Since he won't be sleeping and he's really unhinged, it'll also progressively get less effective as the days pass, which is why it can start wearing off on people before it's actually dispelled.
Basically this means that the longer the spell is in effect, the easier it would be for someone to either break themselves free or, in Zatanna's case, break it with conflicting magic. So she's welcome to give it a shot, and it'll get easier to do it the later into the event that she tries it.
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Well obviously the success or failure of trying to reverse the spell would be up to whoever's character you're trying it on, so assuming you have their permission first:
The magic that's holding the spell together is primarily the Life Force, which is a level above Billy's (who's already kinda godmode), so it's... pretty ridiculously powerful. However, the fact that it's spread across the village, and Billy is inexperienced, PLUS the barrier makes it weaker than usual, means it isn't what it would be in canon. Since he won't be sleeping and he's really unhinged, it'll also progressively get less effective as the days pass, which is why it can start wearing off on people before it's actually dispelled.
Basically this means that the longer the spell is in effect, the easier it would be for someone to either break themselves free or, in Zatanna's case, break it with conflicting magic. So she's welcome to give it a shot, and it'll get easier to do it the later into the event that she tries it.
Hope that helps!