Good Guy Mob
An obvious big bad has revealed himself (maybe he wants to Destroy the World), and it would seem to be in every character in game’s interest to stop him. They rally together, and form the Good Guy Mob.
Good Guy Mobs form due to an out-of-character tendency for players to associate themselves with "legitimate" movements. They are also extremely effective at breaking many in-game challenges, as most resource-constrained rituals and activities can be easily overcome if most of game is pooling its resources together. Nanopunk: Tokyo was a singularly notable example of this and influenced GMs to design games in a way that would be resistant against good guy mobs. However, designing a game effectively against good guy mobs is difficult; even in games where everyone is "some degree of shady", the Sliding Scale of Evil still applies.
If a single character convinces game to form a Good Guy Mob for a Not So Good Reason, it's a Crowning Moment of Bullshit.