If they are not making money on the mod, it’s possible you might be able to get away under a fair use argument, especially if the character skills were some sort of parody.
Although that’s definitely not a legal battle I would want against Disney’s lawyers.
Wouldn’t that make McDonald’s happy meals also gambling? If not explain the franchises that will absolutely refuse to swap toys during certain promotions (Bionics and TY I can think of off the top of my head).