In this case, I can confirm that CaptainSwag is correct. I looked into the BF script for this encounter, and the function for changing the BGM is used at that exact part in the fight. So that's how it's done. Ya gotta set it up in the encounter's BF script. (You can find those in data.cpk/battle/eve...

No problem. We all start somewhere.

Something I probably should have elaborated on last time. Because of the animations not working on models they weren't made for, Atlus made copies of the animation pack for every single battle costume in the game. So if you individually retargeted the animation packs for each edited costume, you can...

Due to an oddity in how the game applies battle animations, if you use ANY model other than the one that the animation pack was made for, then the model will break in battle, as the Picture shows. GFDStudio has a Feature under the Tools tab, called Retarget, that can fix these issues. You'd select t...

A bit of background info: .BMD files are specifically for text and dialogue, and .BF files are basically the game's scripting. But sometimes the game will store a .bmd within a .bf, which makes it easier for the script to interact with the dialogue. There's a tool on this site called "BFMessage...

It is indeed possible! The AtlusScriptCompiler can convert P4G scripts to an editable state and back. You can use the game's own functions to turn flags on and off. The tricky part would be finding which flags make Marie's dungeon available.