It shouldn't involve online games considering some of us don't have the required games. I don't even own MKW, which backs up my point. Something on the forum itself methinks.
Wow, this is a tough one. The only event I can think of where every member could participate in is a competition, but then it would have to be something that anyone could do. For example, you could have a forum-wide competition where participants could submit a photo for judging based on a theme (animals, people, parks, etc). Or a haiku writing contest with a mario/nintendo topic. A committee of volunteers could be formed to narrow the entires down to the final 10 or so and the rest of the MKW community could vote on the best one. Maybe the first place winner could get a special signature created by one of the graphics people???
I don't know. That's just my random suggestion. But I think the idea of holding an event is good one. I hope it works out.