yeah so uhh while i was trying some stuff out with the backgrounds, i notisced something in 1-1
the top bg when edited gives so weird holes and yellow, flags?
here take a look






idk how to remove this so yeah

That is cause you probably imported your custom background into the Peach Castle Grassland one. Well, there is a animation in the flag, which causes those specific pixels to move and that glitches everything if the .png is different (that actually happened to me once, I speak from experience). So if you wanna use your bg maybe import it to a slot in which the existing bg doesn't have animations like that.