Apocalypse and Murder House
This, of course, was one connection we knew to expect going into Apocalypse. Murphy preemptively announced that season eight would be the aforementioned crossover season between Murder House and Coven. So far, the Rubber Man has once again appeared, though we don't know the nature of the spirit. It could be Tate under the rubber, or it could be Ben Harmon. Or perhaps it's possible Michael Langdon simply summoned some kind of Rubber Man demon (like Hotel's Addiction Demon) to do his ill will.
Speaking of Michael Langdon, he's another major connection back to Murder House. Langdon's parents are Tate and Vivien Harmon, the merging of human and spirit. Together, they've allegedly created the Antichrist.