After the secret stage there will be a room with "GOOD!" written in it there is an invisible block maze to get to a hidden warp which leads to a red room. Then after that room is a moving spike wall chasing the kid through a series of jumps. Is there a video on that room because it looks really difficult its about 25x harder than anything else in the game by far.
Screenshot of room:
https://prntscr.com/aqmbfjIf anyone needs my save to see the room i will provide a copy of my save.