Finding their Stats or even their AI would be helpful too, but my main goal is to hack their sprites(Yes, I know about tlp, but normal enemies are not in there, they are most likely compressed and I've seen people talking about how to decompress gba roms in order to get certain things...)
I know nothing about hacking their sprites, but I can tell you that for stats or AI you could download memhack from
www.memoryhacking.com. For stats and AI it might be best to search for the enemy's HP. Stat wise, once you find one enemies max hp, all the rest should be above and below that one, along with other stats like defense, strong to/resist/weak to/absorb, etc.. You just have to figure out the structure to them.
For AI, again max HP should be searched for before you hit the enemu; then hit the enemy, and search for the new HP. Voila, AI found for that enemy; now you just have to figure out the structure here too, as well as where all the AI pointers start, and where they end. It's not hard, but it is time consuming.
Good luck.