I love the idea of Amity Parkers going places and running into trouble and taking care of it themselves because this is normal for them. I also acknowledge that the vast majority of Amity Park's troublemakers can go intangible at will and most of their weaponry is designed to hurt ghosts but not humans.

I therefore submit for your approval the Amity park kid going to Gotham and running into a misc rogue. They unleash the weapons and they don't do shit because the fuckers in Gotham are all human. Technically. Then someone realizes that they are human, not ghosts.

That's when shit gets real, because these kids have a hell of a lot of pent up rage and frustration that they can't just punch the people who keep fucking up their town. This might not be their town, but the assholes attacking them make very satisfying noises when kicked in the nuts.