Hey hey! Have you tried downloading the version I uploaded after this hotfix? https://shaunjs.itch.io/shauns-turn-based-battle-system/devlog/476207/hotfix
I think this should fix your issue. Otherwise the line to fix is in the collision event with oSlime, the last argument "sBGfield" should be the last argument of the function but is accidentally part of the array given as the first argument.