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

Okay, I have it mocked up where Leviathan is just a palette/sprite swap of the Terrato summon, and I can see that utilities are not going to help me much on this one. There are a few limitations:
1. Raiden doesn't have separate animation from Odin, so there's no block of bytes that can simply be overwritten without it affecting Odin too.
2. As far as I can tell, animations have 4 parts. All of the spells happen in part 2, which is used for the summons to display the Esper's picture.
3. We can't re-use many animations, since Leviathan is both wider AND taller than most other Espers. I did a manual edit of the sprite to fit him into the block of sprites called by Terrato. Tritoch is another possibility, but it'll take some finesse.

I've got the location and event edits done. However, I'm getting the ZoneDoctor/FF3usME corruption combo, so I'll have to re-do the work I've done. Any takers yet on the animation edit?

Any takers yet on the animation edit?

I don't have the time but there is no need of certain abilities like spriting or music composition to make an animation. If you can do event, you can do animations as well. I'm not trying to discourage you to get help but in the event nobody is willing to give a hand, you'd be stuck.

Animation have at most 3 script pointers in the animation data (editable in FF3usME). Those two bytes values reference a script in a certain bank (they are all in the same bank, $D8 if my memory is good). There is a near complete commented disassembly made by Everything in the Document section and he made a wiki page with all his findings. Like events, you have hundreds of animation examples in the disassembly.

If there is still free space in the bank you can put your script there or overwrite the one you are replacing given it has an equal or shorter length than the original.

Yep, and I've been able to create new spells no problem, but the Esper animations are just a lot trickier. As a test, I copied every part of Terrato's animation, but used the imported Leviathan sprite. Here are the results.

1. The quake spell does not play in the background. That is somehow tied to Terrato's sprite.
2. Leviathan's sprite shows up behind the enemies, not in front like Terrato.
3. Damage values do not show. Instead, the "cleave" effect plays like it would for Raiden. So the enemy disappears, but is still there. That's somehow tied into the sprite as well.

If I switch the sprite pointer to Terrato, then all 3 of those bugs go away immediately.

If I switch the sprite pointer to Terrato, then all 3 of those bugs go away immediately.

Yes this sounds a bell. While doing monster expansion, I found one code piece per espers but having as ID their monster / sprite ID (384 + esper ID) in upper $C2 which is a continuation of bank $C1. I had to change all of them to prevent buggy esper call since I was expanding monsters number by 128. There are a few $C1 call for each piece of code and I believe it's something GFX related for the least. Leet Sketcher has a good upper $C2 disassembly but sadly bank $C1 is almost not commented. Here are the places where there is a "LDX monster / sprite ID" for all espers. This could maybe lead to a solution if you isolate and understand Terrato functions calls.

Code:

org $C2EB52
org $C2EB69
org $C2EBC2
org $C2EBE1
org $C2EBEE
org $C2EC01
org $C2EC1C
org $C2EC29
org $C2EC36
org $C2F020
org $C2F073
org $C2F08E
org $C2F0C1
org $C2F0E2
org $C2F0F9
org $C2F109
org $C2F119
org $C2F129
org $C2F14D
org $C2F16B
org $C2F195
org $C2F203
org $C2F211
org $C2F221
org $C2F231
org $C2F24D
org $C2F27B
org $C2F289

Edit: I could probably spend some time on this to verify my theory and since you're not (yet) an ASM guy. I have a school project due next week and an exam but next weekend I should probably be able to allow myself an hour or two on this.