WheatleyTheMoron

I'd like to change overworld items in BW, like the thunder stone in Chargestone cave, and I understand it's an NPC that calls a script from outside the map's script file, but I'm not sure how it calls the script exactly, where the script it calls is or how to change it. A similar thing happens with trainers too if I were to guess. I just haven't seen much about that online. If anyone has anything to share regarding this, that'd be great.