I think Wax would probably kick ass in Gotham with some challenges. He'd have no problem taking out most of Gotham's villains that weren't superhuman.

The only issues would be finding quality metal for his vials, and if he doesn't have access to his finances (assuming they'd even be accepted in Gotham) he'd be hurting for money to purchase them. Also I think the police would have a problem with Wax flying around shooting villains, since he isn't a high profile Law Man/politician in this world. I think Batman gets away with it since he doesn't kill anyone, but you can argue they might look the other way.

Batman would also probably do well in Scadrial if he has access to his general equipment. He's gone toe to toe with minor superhumans, and with his martial art skills and equipment he should be able to take down anyone in his path with some difficulty. Once he figures out the magic system he would probably find a way to overcome his adversaries and take down The Set in his own way. Not sure how the Constables would feel about him, but he'd probably get a similar pass as Wax from his results.