Is AHS Apocalypse a crossover?
Yes,
Apocalypse was designed to be a Murder House/Coven crossover, but it also managed to be a Hotel crossover, too! ... Eventually, Michael demonstrates his magical abilities by saving Queenie from the hotel and reuniting her with her coven, and she remains a major player as Apocalypse plays out.
Who is the most powerful witch in American Horror Story?
Fiona Goode
American Horror Story - Coven, Season 3 -
Fiona Goode, the most powerful witch of their generation, returns to town, reigniting old rivalries with the Coven's deadly enemies, the Voodoo.