One of my friends is running a game, and I've been playing in it as an NPC from one faction working with the PC's faction
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basically every era there's a contest among the fey to choose the new archfey, basically god, and it's done in a ten year competition to enact the greatest change in the world. there's a faction for each alignment, and the fey in the running can't directly interfere with other teams. Each fey chooses a champion, and others to round out their teams, they have to have at least 5 people alive at the end to qualify, if the fey or their champion dies they're out, and they can swear themselves to another faction, which gives that faction all the "points" they've earned so far
my faction was lawful/evil, the party's is chaotic/good. you'd think that wouldn't work, except the big bad is a psychotic death fey who started a zombie plague and unleashed an army of tyranid-esk horrors on the world, and wiped out most of the human race in under a year
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the party didn't know i was with L/E for 2 or 3 sessions, thanks to my kickass bluff skill. my job, as it was, was to determine if they're group was strong enough to warrant allying with. (official report: they're strong but freakin' stupid) once I revealed myself I was kept at arms length from most sensitive information, which I found out anyway because I that good. and have a power that can crap out people's mental stats. also they made me promise not to tell my faction anything I learned while with them-I sent daily reports via mental link anyway

the party survived (along with most surviving humans) on a flotilla of salvaged navy ships, going around the world collecting survivors where they could and fighting back how they could.
They knew where the big bad's champion was, but refused to go after him because he was mostly a confused kid, which is stupid because just kill the little f*er and you take out the biggest threat to winning the competition, not to mention the dude who's trying to end life as we know it
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here's the important part: I was actually trying to get my faction to win. not because the DM wanted me to, he was planning to merge the factions, but because
I wanted it. I had plans to wait until the other threats were dealt with and then kill the party's champion and steal the win out from under them

so, after about 4 months in game time, I got bored. I got into their records (1 stealth check) and found out where the kid was, and promptly sent this information to my group. and they went there in force, 50 of the strongest people on the planet. the DM rolls for how well they do, and I learned a few things. 1. the big bad was in the same place as his champion.
2. he apparently ate nuclear energy, and had quite a bit undigested
3. 50 badasses is enough to kill the big bad, and almost derail the entire rest of the campaign if there wasn't one other faction left
the bad news: he exploded in his death throes, taking out arizona, parts of utah and nevada, setting souther california on fire, the explosion set off the yellowstone super volcano, which set off the ring of fire
the good news: they captured the kid alive, and with everything blowing up like that, they racked up so many "points" they effectively solidified their standing in first place
bad news: only the fey and champion survived, plus me, so there weren't enough people to qualify, and those two were being chased my a horde of monsters basically the entire length of south america
good news: I secretly managed to recruit about 500 people from the survivors, so if they lived we totally could pull it off
bad news: the party rescued them and the fey decided to swear allegiance to the party's faction, effectively ending my dream of total victory