While any Koopa is in their kicking animation (including to flip a shell over), they will not be affected by gravity and won't move with the layer they're standing on. When on a scrolling Layer 2, this can cause them to end up inside the layer, as well. ... https://www.youtube.com/watch?v=BlXOh7zz8E8
The wallspringboard's hitbox loops every 256 pixels. By scrolling the screen I warp the springboard around the screen. You can even clip through the floor with it.
...
https://www.youtube.com/watch?v=L09M8niugq0