With the older emulator I was using (No$GBA 2.6a)
all custom spell animations I made would play at their proper speed and settings for each frame.
Same now, if I launch the older No$GBA version the spell frames will still play at proper speeds
despite a ROMhack having being updated many times.
However, with No$GBA2.9 all frames play at the same fast speed
knocking off the spell timings and their sounds.
Basically, my older spell animations are all out of sync with their sounds and frames.
Many emulators handle sound independantly of the gameplay speed, it might have something to do with that, it might also just be that one of the emulators is “uncapped”, instead of lagging like a real gba would it handles everything in a single frame, making the animation faster.
There’s also differences on how emulators handle transparency and affine transformations.
I wouldn’t worry too much about how different emulators play different stuff, emulators are often very innacurate, there’s no reason to worry about your hack working in all of them, just make sure it works on a GBA, anything else is the fault of the emulator, if it doesn’t work it’s on the user to find an emulator that actually emulates properly.