If you're talking about on FD, you up B with most of your momentum sliding up the lip, and when its just about to run out you DI towards the ledge to sweetspot but it does an instant release thing with SJR IIRC, kinda like wolf's side B.. it also works with her grapple sometimes.
as for the morphbounce, it looks like he started with a dash to the very edge of the platform, drops through, plants a bomb perfectly on the platform (note the minimal bouncing of the bomb), DIs almost if not completely backwards, and RIGHT as he should touch the ground and land, the morphball animation frames end and he's propeled upwards even BEFORE he SJs, as noted by the height of the SJ ripple. I'm thinking the input is something opposite of the Raigoth cancel because holding down would just make you FF to land. After talking with rohins about it he said he can do it sometimes and he taps up and jump to get it to work, but he nor I are quite exactly sure how to do it perfectly.
Note that the physics of dropping through a platform are drastically different than just jumping and landing or fastfalling, because she undergoes a different animation and is propelled differently. She also lands with a different, more laggy, animation. Because bombs can cancel animations AND their momenta (for example, in the tips/tricks thread I discuss ledgejump bombs canceling the jump), the platform dropping might be the essential component of this tech.
If only it could be done from a normal jump bomb, it would have insane applications in terms of spacing, setups and mindgames.
It's too frustrating because I think it's veeeery frame specific, much like the ISJR, and because the sequence of events presented have rather technically difficult steps anyway, it'll be a challenge for us to reproduce it..
but try anyway.