I discovered a trick when playing around with sandbag.
So first, theres the trick where if you are thrown with a hit stun you can press the shield button when hitting the ground to quickly recover. You can do this either stationary or rolling. Then you can also use this when hitting a wall or ceiling to cancel all momentum when going to it. And so when you use sandbag, you can use his recovery to launch him into a wall or ceiling and cancel momentum. Using this, you can have him go under many stages, and in
https://www.mediafire.com/file/mmm1qhb7iv0cfii/sand%20bag%20trick.ssfrec (open it in ssf2 replay), I use this trick to go under sector z ship. Also, important, you want to press your shield button right after your bomb hits and you will hit the ceiling right.