Hello, this is my first post in here.
I wanted to make a NSMB Hack and I wanted to use the final castle's upside-down mechanic for a few levels, but I don't understand how it works (for example if it's handled with special sprites or maybe if it's asm coded).
Thank you everyone in advance for your answers!

(I'm sorry for not-so-fluent english, I'm not a native speaker)

Good question! Maybe if you try to add a switch in a place and do tests? I belive enemies doesn't switch. Oh and I'm not sure, but you need a specific tileset or a sprite you need to enable.

I want too to do this in my hack (link in description), and I already did projects like this in Scratch.

(No ASM code, but your english is good for me (even if I am not english too))