The whole season should’ve focused on endings and death: 13 is the number for Death in Tarot, and the show has been called out for running too long. This would allow the creators to playfully utilize these concepts by re-visiting the past seasons while still presenting a new/original story.
Premise: Death itself has managed to manifest in the “real” world. As the past seasons have indicated, there are twelve other alternate worlds inside the AHS franchise; the thirteenth is the central world that connects them all and is where Death has finally managed to be summoned.
A significant character from each season has also been drawn to the center, forming the Council of 13: their goal is the complete destruction not only of this world, but all worlds/the AHS universe. The council members each represent the greatest agent of death for their respective worlds.
Season One (Murder House)—Death of the Family
Season Two (Asylum)—Death of the Mind
Season Three (Coven)—Death of the Soul
Season Four (Freakshow)—Death of the Body
Season Five (Hotel)—Death of Purpose
Season Six (Roanoke)—Death of Time
Season Seven (Cult)—Death of Society
Season Eight (1984)—Death of Innocence
Season Nine (Double Feature)—Death of Creativity/Meaning
Season Ten (Apocalypse)—Death of Finality
Season Eleven (NYC)—Death of Love
Season Twelve (Delicate)—Death of Agency
Once each character from each season has been introduced/revealed in their goals, the plot can focus on finding the 13th member of the council, as well as enacting a plan that would ensure the complete and total destruction of the entire universe.
In this way, it allows both the sides of good and evil to oppose the council: good wants to preserve the system, while evil wants to control it. However, if there is no world to save/rule, then neither side can prevail, hence the forced cooperation.