Okay so for those of you that don't know XCrawl... what the fuck, man.
It's this third-party D&D setting from about 10 years ago that is like a cross between regular D&D, pro wrestling, and the movie version of The Running Man. It's bizarre, the art is hideous, and it's about the funniest thing in the world. And a new edition for Pathfinder is coming out pretty soon. But I'm not here to shill that.
I'm here to talk about the one cool mechanic from it, one I don't mind including in my other games on a regular: The Mojo pool.
Basically the way it works is it represents the party's teamwork and exhortations bringing the best out in each other. At the start of the session everyone rolls 1d6 and add up the total, which can never be more than 12. At any time one player can grant another as big of a mojo bonus as she likes to any attack, save, or skill roll, with no limitation other than the amount presently in the pool. There's just one catch: You're not allowed to ask a fellow player for a mojo bonus, they have to offer it to you themselves. If you roll a natural 20 the mojo they offered is not subtracted from the pool, instead you add an extra point of it, but if you roll a natural 1, two extra points are deducted from the pool. Also, particularly well-coordinated groups of NPCs or monsters can also have their own mojo pools.