Speaking of boss monsters, I've had a couple of ideas for monster characters which could be implemented later on:
-Something akin to the River Person in Undertale's Underground, whose job it is to ferry people between those areas of the Underground with water, and in particular to grant those without gills the protection needed to enter the submerged city. May or may not be a robot disguising itself as a cloaked entity, which in turn may or may not be a floating skeleton skull disguising itself as a robot. Details of such to be established.
-Fistrocket, a being with rockets for fists. No relation whatsoever to the fairly common Fistrocks in the area he lives, like seriously guys, who keeps spreading that rumour that he's the Fistrock father? Come on. Given that N.A.U.T.I.L.U.S. now exists, I'm probably not going to make this guy.
-Lord Ceilingfortress, one of the other Boss Monsters remaining in the Underground. So called because he is, in fact, a gigantic metal fortress that crawls across the ceiling of the Underground wherever he can, and in turn contains a great many lesser monsters who live inside and/or traverse to him. Or maybe he's just piloting a giant metal fortress, but all the evidence so far suggests that it's him, he is the fortress.
If somebody wants to steal one of these ideas for their character, feel free; otherwise, I may or may not write up their sheets at some point.