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

The exact cut-off between an AU qualifying as a Special Event, and an AU qualifying as a Post-Genocide Sequel is the world being destroyed. In Undertale, during the final cutscene of the genocide route, the screen must be consumed by nines and the game close a few seconds later for the AU to qualify as a Post-Genocide Sequel. If an event happens while Frisk and Chara are initially talking (such as Frisk just resetting), then the AU is a Special Event. However, if an event happens while Frisk and Chara are talking in the abyss (open up the game while system_information_962 is in your appdata UNDERTALE folder), then the AU is a Post-Genocide Sequel. If, however, the game continues after the player sells their SOUL (open up the game while system_information_963 is in your appdata UNDERTALE folder), then it's a Special Event. If Frisk then continues on to achieve the conditions required for a Post-Pacifist Sequel when the Post-Genocide Sequel requirements have been previously met, then the AU is a Post-Genocide Sequel.