Secret Wars (1984) and Contest of Champions (1983), but then there was DC's twelve-issue “maxi-series” Crisis on Infinite Earths. Even though I was primarily a Marvel fan at the time, Crisis was out “epic-ing” everything that had come before.
In this environment, my cousin and I hit upon the idea of doing a multi-game crossover campaign. At the time, our repertoire included AD&D, Gamma World, and Villains and Vigilantes. We planned to include them all, with one of the two of us on DM/GM duties.
Unlike comic book crossovers, I don’t think it was our plan to have characters meet up--we weren’t interested in that conversion task. Instead, there would be some threat affecting the “multiverse” we took for granted that all our game world’s inhabited. I think the basic idea was borrowed from the plot of Crisis--there would be some sort of device (like the Monitor’s pylons in the early issues) that the characters had to defend to keep their world safe. Or maybe, there was some item they had to find first. Maybe we talked about different ideas at different times, I don’t fully recall.
In any case, we never did it. Maybe just because we never got around to it, or maybe we decided it would be more fun to plan than to play. I think I did run an AD&D game once were the character's glimpsed their other character's in different game-worlds in the mirrors of an evil sorcerer's sanctum, so I didn't entirely give up on the multiverse idea.
Anybody else every attempted a cross-game crossover, or at least thought about it?
2 hours ago