Oh my god, that was the issue-- script calls and just any complicated script is really new to me and beyond my element. I literally did the full rpgmaker mv tutorials 2 days ago, and thought that making a character speed mechanic would be a simple first task on my own LOL. Anyways I did some googling and guessing, and found what I think is the leader script call that was supposed to go there, and it seems to have fixed the game crash issue.

Does this look right? Is there anything else I should do with that?

