Hey FYI to other modders, if your custom character fails to render and crashes the game, try checking the logs! They’re in the Roaming folder in AppData under a folder called "Snivy". Should just be a log.txt file.
If you're having the same problem I was, there will be a line that says something similar to "Failed to initialize texture from PhysicsFS path: character.zip/gfx/character\character.png". This means you need to open the character's main anm2 file in a text editor and correct a line by changing a "\" in a filepath to "/"!