I really wonder why you made a special inventory GUI, why could you not just add them to the normal inventory? It makes it much easier, and you need to use 1 key less.
Did you do this to prevent changing base classes? If so then I understand, if not I would really like this to be in the default GUI
Did you do this to prevent changing base classes? If so then I understand, if not I would really like this to be in the default GUI