All-Star Cast: While they already had Jessica Lange, this is the season where the number of Oscar winners and nominees exploded. They have two winners (Jessica Lange and Kathy Bates) and two nominees (Angela Bassett and Gabourey Sidibenote Precious, from the movie adaptation of Push, about an illiterate, overweight teenage girl trying to escape the physical, sexual, and mental abuse from her parents). You could argue this is actually a case of Unfortunate Implications, because all four have factors working against them, that likely made them cheaper to cast. Lange and Bates are both aging actresses (which is considered poison in the youth-obsessed Hollywood), Bates and Sidibe are both not traditionally attractive (read: not thin), and Sidibe and Bassett are both African-American women (who are already typecast and marginalized enough outside of Hollywood).
Since the Turn of the Millennium, TV productions have become more ambitious and more sophisticated, while movie rolls have become more sparse and less character-oriented. Arguably, TV, especially cable TV, has been offering more satisfying opportunities for character actors.
Casting Gag: As in Asylum, the creators love to re-cast the actors in roles playing off their previous characters.
In Murder House, Evan Peters tries and fails to save Taissa Farmiga, but the house resurrects her as a ghost. In Coven, Taissa tries and fails to save Evan, but her friend resurrects him as a zombie.
In Asylum, Peters eventually ends up in a three-way relationship with two women, with two of the three having been resurrected from the dead. In Coven, he again winds up in a three way relationship with two different women, again with two of the three having been resurrected.
In Asylum, Sarah Paulson is raped by Dr. Threadson, and spends the remainder of the season trying unsuccessfully to abort his child, who grows up to be evil. In Coven, she is barren and tries unsuccessfully to cast a fertility spell.
In Asylum, Lily Rabe plays Sister Eunice, who was possessed by the Devil, and ultimately killed and then cremated. In Coven, she plays Misty Day, and her first scene is her character being accused of demonic possession and being burned alive.
In Murder House, Jessica Lange (Constance) and Jaime Brewer(Adelaide) play mother and daughter, respectively, and when Adelaide dies from a hit-and-run, Constance is grief stricken. However, in Coven, evil Fiona(Lange) is the Supreme witch, a leader and mother figure of sorts, to Nan(Brewer). Fiona ends up drowning Nan in cold blood to use her soul for a sacrifice.
In Murder House, Alexandra Breckenridge (Young Moira) dies from a bullet to the head after a married man tries to rape her and his wife catches them. In Coven, the married man is her lover, she doesn't know he's married, and he's the one who kills herï¿½ by shooting her in the head.
Both of Denis O'Hare's characters are physically deformed (burn scars in Murder House and no tongue in Coven) and in love with Jessica Lange. Who takes advantage of them, using them as her Igor.
In Murder House, Jamie Brewer's character Adelaide (who lives next door to the main characters) is locked in a closet by her mother as punishment. In Coven, Nan finds Luke (who lives next door to the main characters) locked in the closet by his own abusive mother.
In Asylum, Evan Peters' character Kit takes in a sick and out-of-her mind Jude out of his good heart and his children restore her her sanity. In Coven Fiona seemingly restores Kyle's mind, but it's suggested her intentions are much less altruistic.
Not a specific actor but both Murder House and Coven have the spirit of a dead killer residing in the house, who falls in love with one of the girls that moves in.
In "Murder House," they put Taissa Farmiga in a lot of hats. In "Coven," they put her in even more.
Dawson Casting: While not dealing with teenagers, the real Marie Laveau would have been in her 30s when Madame LaLaurie's crimes were discovered. She's played by Angela Bassett, who is in her 50s.
Also not dealing with teenagers per se but Misty Day is said to be not too much older than the other girls, making her late teens/early twenties. She is played but Lily Rabe, who was in her early 30s at the time of filming.
What Could Have Been: There were apparently talks to give Coven a spin-off series, but Ryan Murphy ultimately decided to wrap up everything in this season. This would likely explain why there was so much word-building put in that wasn't touched, and several arcs being cut short. Notably, Ryan Murphy is now making a separate show that seems to be the Spiritual Successor to Coven, Scream Queens.
Episode 9 "Head" was the second time an FX series closed an episode with some version of the song "Oh Freedom". Sons of Anarchy closed their season two episode "Falx Cerebri" with a choir version of the same song.