Post-Pacifist Sequel AUs are AUs that take place after the Pacifist Route of Undertale.

The exact cut-off between an AU qualifying as a Special Event, and an AU qualifying as a Post-Pacifist Sequel is the Monsters leaving the Underground. In Undertale, after defeating Asriel Dreemurr, Frisk must go through the final door that leads to the surface for the AU to qualify as a Post-Pacifist Sequel. If an event happens during the epilogue of Frisk wandering the Underground, talking to the Monsters, then the AU is a Special Event. However, if an event happens while Frisk and the six Monsters in the cutscene are looking out at the sun over the landscape, then the AU is a Post-Pacifist Sequel.