It's the original Venusaur sprite, I just saved it from unLZ and imported it without messing with it. One thing is, when I import Venusaur into APSE and Synchronize Palettes, the colors are a little messed up, but then I just import it again right after and it clears up all the imperfections. Don't really understand why that is but ok.
I've been importing it one by one thus far.
I've tried changing the most minor things (like changing a light purple color in a shiny palette to white) and it still gives me that unhandled exception error when I Write to ROM.
(thanks for the extensive help btw)
Aha! Now I know what the problem is! (Sorry for the late reply. I had to sleep too.) What you should do is take a clean FR ROM, Open it with APSE, export the Venusaur sprite (File>Export) Then open the ROM you are using and import the Venusaur sprite you exported earlier. Hope it helps. It works for me always.