Beat the demo. It was fun.
There was a duck boss, then a non-interactable skeleton boss in the top right of the map in a secret area. He couldn't hurt me nor I him, and then he just repeated his attack animation rightwards until he reached the edge of the room and reversed the left ad infinitum. It was where the game says "this area under development". Is that not supposed to happen? If there's another skeleton boss, I missed it.