You lawyer up or move on. It sounds to me a part of you wants to get even because Nintendo sent you a C&D and you want justice that Nintendo should do the same for these other guys. Putting aside the merits of right and wrong, its childish if this is actually the case.

You have a right to defend your open source project and if you really want to get these guys to follow the rules, enforce it. But don't expect Nintendo to do anything. If they do, its great. You did your part in reporting this (albeit you probably wouldn't if it wasn't your project specific maybe; I'm totally guessing on this part).

But if it bothers you that much, have an attorney send them a letter.