This code will make the current submap move up and down, like a floating island. Original code by yoshicookiezeus, I optimized it and made it work in any submap.
Note: this code works better in Yoshi's Island and Valley of Bowser. Other submaps are 8 pixels shorter, which causes the bottom row of the adjacent map to be visible when the OW scrolls down. You can avoid this issue by having empty tiles on that row.
Unfortunate that this doesn't work on the main map, but this specifically mentions compatibility with submaps (not main) so it's still being accepted. Hopefully a workaround for the main map could be done in the future!