If you didn't know, the "Antichrist" is actually a biblical reference to the Book of Revelation. It's the last book of the Bible, and it describes to Apocalypse. Religious imagery has pervaded quite a few seasons of American Horror Story. Obviously, all the Antichrist talk happens in Murder House, but Asylum is saturated in religion, and there are breadcrumbs in other seasons as well. This is why it may be interesting to use the Book of Revelation as potential inspiration for AHS: Apocalypse.
In this book, the Antichrist is described, at times, as a seven-headed Beast. There's a full PDF version of the book courtesy of the Geneva Bible online. Prepare yourself, it's pretty dense stuff.
"I saw a beast rise out of the sea, having seven heads, and ten horns, and upon his horns were ten crowns, and upon his heads the name of blasphemy. And the beast which I saw was like a leopard, and his feet like a bear, and his mouth as the mouth of a lion; and the dragon gave him his power and his throne, and great authority. And I saw one of his heads as it were wounded to death, but his deadly wound as healed, and all the world wondered and followed the beast."
I'm not saying AHS will literally create a seven-headed beast — don't rule it out, though! — but there is clearly fodder for some nightmarish imagery. There are also lots of other interesting aspects to incorporate: the Four Horsemen of the Apocalypse, the Whore of Babylon, and more. I could imagine a gripping season in which Murphy finds modern-day ways to depict these ancient images.