Eliminated players continue as vassal players

The game "Viktory 2" has a vassal system, where the player get it's "freedom" but cannot attack it's master unless free by another player.

I did not have a chance to play much with this mechanic, but it did not ended well because the vassal player had no reason to support it's master.

So maybe there should be some sort of motivation to help and support the master.

The other solution that might not fit with your game, is when the 1st player is eliminated, the game ends.

The idea of a competitive game that develops into a co-op has got my gears turning... I'll be watching this thread. :)

As far as motivation goes, I'd narrow down what motivates players in co-op and team games. Joint victory, puzzle solving, etc. The subordinate/master player mechanic probably has some unique hurdles...

I've played a lot of Sentinels of the Multiverse and the knocked out powers always seemed a bit lame for the affected player. Like most co-ops, it can suffer from alpha gamers or well-meaning player's narrowing down your decisions for you. When you have a hand of hidden cards, it's hard for you team to micro-manage your decisions. When you're dead, in my experience, every other player discusses which power the dead player should use while the dead player tunes out or leaves the table. Either way, they become a second-class player.

My main concern with a vassal character is that their autonomy stays intact and their decisions stay meaningful while still making sense within the master/vassal theme. It might be hard to find a balance but I'm sure you can think of something.

X3M's vengeful spirits idea (or vengeful disembodied brains if you wanted a more sci-fi themed game) would have the advantage that it won't cause a runaway victory, which could happen with the original vassal idea - each time the leader defeats another player, he effectively increases his strength as well as having one less enemy to deal with.

If you want to stay with the vassal idea, then perhaps instead of becoming the vassal of the player who defeated them, they could aid the weakest player at the time when they were conquered.

Although in my personal opinion (which I don't expect many others to share), player eliminiation shouldn't be automatically ruled out for a game design. I understand why it is considered a flaw in the euro-game design philosophy, but that is just one approach to game design; a good one perhaps, but it doesn't automatically invalidate all others. There are some people who enjoy that sort of thing (sometimes I'm one of them), and it is probably more in keeping with the theme for a game involving ruthless supervillians.

I use submission rules in fairly long strategic "empires" games. Players can submit long before they're actually eliminated. Including rules for "unsubmitting" though that's very rare.

Of course, Britannia has specific rules for certain submissions, but that's historical as well as practical.

I don't see much hope for submission in low-level tactical games.