The more I think about the rules, the less I understand how this could work at all. How can you remix a game without using assets from the game to make it obvious what you're doing?
The reason for the rule is more to prevent a DMCA takedown of a submission for unauthorized use of assets. If you are riffing on the themes of a game, you might not need to use the original assets to bring across that theme. That said, I'm not going to enforce the rule, but I'd be negligent if I didn't have it there.