Pony Fantasy VI Remake

I can confirm changing the field palette does nothing, tried it to see.

You're not confirming anything since you don't know where the palette table (or index) is located if any. You're stating that it can't be changed with FF3usME, which we all know because there's a message saying so in the editor. Palettes are located at $E68000, there's a few places it is loaded in bank $C0 based on a X index but I don't have the time to trace for you where the X index is calculated, if based on a table like I was talking a few posts back. This is for overwold palette, I'm not sure if it is set differently in battle for that specific sprite.

Edit: there might also be an branching based on sprite ID like Catone says.