"Raiden to Leviathan?" and "New Battlefield?"

As I'm putting together the  project charter for the next phase of my project, there are 2 outstanding questions that I've never heard answered on these forums. [Disclaimer: I have no illusions about my own ability in these matters. With no training in any computer science and little to no experience in ASM, I struggle for hours to make modifications that more experienced members around here could probably code over breakfast. I hope I've been around long enough for you all to know that I don't hold that as an excuse; it's just a recognition of my own limitation.]

Raiden to Leviathan
Of all of the material from FFVI Advance/iOS/Steam that I want to "port back" to the SNES version, the esper Leviathan and the spell Flood are at the top of the list. The easiest way, as I see this, is to combine Odin/Raiden into Odin's esper, only gained after the queen's tear, and overwrite Raiden with Leviathan. I can add Flood through MMMMMagic, which I planned to use anyway to give a 13th spell list. For the Esper, I believe I can do the sprite through FF3SE, and I can edit the spell damage data through FF3usME, but how do I edit the animation? I'd like to keep it simple: Leviathan shows up, casts "Cleansweep/Tsunami" in the background, and disappears. Does anyone have experience with this?

New Battlefield
From ZoneDoctorCE, it appears that there are two blank battlefields between "48 - Airship Deck" and "51 - Final Battle 1st Tier". I'd like to add an "Aquatic Cave" for use in the Cave to the Ancient Castle and possibly Hidon's Cave. The actual background could be a palette swap of the standard cave background, but the key is that it would be possible to learn the dance "Water Rondo" from this battlefield. Like above, has anybody ever tried this?

Thanks for your thoughts on this.

UPDATE: Aquatic Caves Patch Download: 

 aquatic caves.zip (1.52 KB, 5 downloads)