For some reason when I select an image for an event, B and C tilesets aren't in the list (they are supposed to be the last two, under BigMonster). I think it's the issue with the Standalone Jam version of RPG Maker MZ.
Redownload the Game Jam version, uninstall the version you currently have installed, and reinstall it. This was a bug in 1.3.0 which was what the initial Game Jam version was. The Game Jam version has been updated since then.
