I've been thinking in terms of meta-games, and that led me to a way to connect a series of otherwise disparate campaigns, mini-campaigns, and one-shots as part of a cosmic, meta-versal struggle between good and evil (or something similar, like order and chaos).

Before I get into the details, I have a few disclaimers:

1. This is a brainstorm from me, not something I've actually done. As such, haven't playtested it or worked any of the bugs out. Use at your own risk. No warranties should be implied, and your mileage may vary.
2. This will really only work for a group that is interested in playing different games (settings, even systems), through a series of one-shots, mini-campaigns, and (optionally) full-length campaigns. A group that only plays D&D 4th might have little use for this, although they could use it if they played new groups of characters in all the different D&D settings available (Eberron, Greyhawk, Ravenloft, Spelljammer, Dark Sun, etc.).
3. I think you'll get the most interesting results out of this if your group is willing to play across quite different settings and systems, and play to the expectations of each new game. Play Vampire: the Masquerade as Vampire: the Masquerade, play OD&D as OD&D, play D&D 4th as D&D 4th, play Shadowrun as Shadowrun, play Dogs in the Vineyard as Dogs in the Vineyard, etc., with all the expectations, limitations, and styles therein.

The Champions

Archetypical Champions (I'd call them Eternal Champions, but I think Michael Moorcock beat me to it) move between worlds, inhabiting/joining with/possessing/parasiting local heroes, fighting a war that could affect all the realities.

These champions can be full-fledged characters, at which point they're literally possessing people from world to world, or they can be abstract ideas, such as Strength, Family, or Hunger for Knowledge, at which point they are merely empowering their representatives on each world.

If the champions are characters, then they may struggle with the question of whether the war is right, if they're really on the right side, and does the war justify the wreckage they leave behind them when they jump in and out of people's lives. You might look to Marvel's Exiles, written by Judd Winick, for ideas in this case. The key to making this emotionally relevant is to make sure the new game characters have personalities, histories, and families, hopes desires, dreams, fears, beyond what the champions bring to the table.

If the champions are abstract ideas, the moral questions are minimized, as is the sense that you're playing a character who is, himself playing a character. Instead, continuity can be preserved by making sure that each player's characters stand as representatives of the same abstract idea. If the player's Champion Idea is Strength, then that should hold across her characters across different games.

Of course, you can have a tremendous amount of difference between characters with the same icon. Superman, the Hulk, and Fezzik could all be icons of physical strength, but they are all very different characters. For that matter, so are Wonder Woman, She-Hulk, and Ginormica (from Monsters vs. Aliens). Heck, Princess Fiona even embodies this in a couple of Shrek movies. In other words, you have a lot of options for each new game's character, even sticking to the same abstract concept.

The Champion of an ideal doesn't have to be the person whose stats in that idea are highest, even assuming the idea is something like Strength that can be measured by game stats. The Champion just needs to have a strong devotion to that ideal. For example, the Strength Champion in a Shadowrun game might not even be the strongest person on the team, if he or she is strong through natural means and gets out-muscled by cyborgs.

With that in mind, the Strength champion of a superhero game might be an unaltered, but extremely dedicated, human, like Wildcat (Ted Grant) from DC's Justice Society of America. In many ways, a dedicated heavyweight boxer turned costumed crimefighter embodies strength better than someone who gained superhuman strength through a metahuman origin story.

Bringing the Characters In

If the champions are actually characters themselves, you should start with them knowing that. If they all came from the same game-world (say, you decided to end an ongoing campaign by having those characters become the champions and moving into the meta-campaign), you can begin with the reveal and then have them “leap” into the new game, and the new characters.

If they come from different settings, you could have them meet in a neutral, “nowhere” place, have just enough time to get to know each other (and realize they can't kill each other in the “nowhere” place), and then get zapped into the new game. In this case, I strongly recommend reading Judd Winick's run of Exiles, at least the first two or three issues.

If the Champions are abstract ideals, then you should simply begin a game, and go from there. The players know what ideal to make their characters embody, so you should be able to just go.

There is another option, which is one that can be fun if your players like surprises. You can have one game end, then start another. In the other, make sure to echo events from the first, subtly. Lay down clues over a series of mini-campaigns and one-shots that will lead the players to realize they're all connected. Of course, you'll have to give them some way to use this information, possibly to bring the characters together to permanently defeat a great evil by attacking it from across the different universes at once.

If you want to integrate this into an ongoing, long-running campaign, you can do it by running some “vacation” games, one-shots or mini-campaigns that aren't the main one, just as a break. But have the events in the main game echo into the “break” games, and have the events in the “break” games echo back.

For example, in a long-running fantasy game, lets say the PCs slew an entire orc army, or a great dragon or other mystical beast. Then, you take a break and play a more modern horror game, in which a great blood sacrifice has awakened a great horror, or else the guardian that kept it contained has been slain. In that game, the investigators manage to bind or destroy the horror. Returning to the main campaign, the PCs learn that an evil god has died, or been bound, and its clerics are powerless. But when its time for the next “break” game, the PC's stumble across the evil god's last act, a trap that curses them, sending them into a survival horror game, in the bodies of weak and normal humans facing a zombie apocalypse. And so on...

Next month, I'll get into more detail about methods, including ways to handle the advancement of champions, carrying that advancement between games, champion death, and replacing champions as players come and go from a campaign. I'll also brainstorm a little about planning what to do if the players fail or succeed in any given one-shot, as well as planning out the broad strokes of the meta-campaign in advance.