As a teenager in the 1950s, Mary Eunice attended a pool party which resulted in a skinny-dipping prank, which left her exposed.
Personality and Appearance
Mary Eunice is an attractive young woman, With blue eyes, but due to the devil's possession, her eyes sometimes flash a bright orange.
Before the exorcism and death of Jed Potter, Mary Eunice was shy and innocent, and she feared Sister Jude's strict personality. She put much trust in Dr. Arden, despite questioning the nature of his activities. After The Devil's possession of her, she becomes evil and sadistic, trying to take over Briarcliff and murdering the staff and inmates to do so.
Sr. Mary Eunice greets the visiting Lana and warns her about Pepper's violent nature. She escorts Lana to the administrator's office, where she interrupts Sr. Jude in the act of punishing Shelley and is severely chastised for her failure to knock. She forgets her lesson within minutes, as she bursts in again to announce the arrival of "the bad person" to Briarcliff Manor.
After dark, Dr. Arden sends her into the woods to feed some mysterious creatures, she meets Lana, who blackmails her into allowing her into the asylum. After Spivey tosses his feces at her, she confesses to Sr. Jude her part in allowing Lana entry. Sr. Jude berates her stupidity and Sr. Mary Eunice bends over her desk, begging for punishment. Sr. Jude is shocked into pity and smacks her ass before dismissing her from the office.
Upon Jed's death after a lengthy exorcism, she becomes the new host for the demon that possessed him. After which, Sr. Mary Eunice seems a new woman, now rather sly and manipulative. She taunts Sr. Jude with a newspaper from 1949 about the little girl Sr. Jude killed in a drunk-driving accident, propositions Dr. Arden, and kills an inmate before feeding her corpse to Arden's creatures. During the showing of The Sign of the Cross, she gleefully awaits the scene in which the Christians are fed to the lions.
She picks out a cane from Sr. Jude's closet for the punishment of Kit and Grace after they are both caught trying to escape.  Sr. Jude is impressed by the improvement in her demeanor and slightly baffled. From this point forward Eunice begins to further toy, manipulate, and put together some sort of plan that involves eventually gaining control of the Vatican. 
She slowly goes from being discreetly mischievous to unabashedly cruel openly to everyone who she has outwitted, including Sister Jude. During the head Administrators investigation of Arden, Eunice strings together events that send Jude into a downward spiral. Things including setting her up for murder, threats to reveal her checkered past, and when she is removed as head of the asylum Sister Mary Eunice quickly takes Judy's place.
As the head of the Asylum Eunice begins her unorthodox rule over the asylum, delighting in having free reign over the establishment. It's not too late after this inauguration that the Demon inside Mary finds itself confronted by a Holy Host. An inmate suffering from schizophrenia is at the end of his rope and, through some gruesome off-screen antics, summons the entity known as Shachath. In the inmate's room this Angel of Death gives him the kiss of death, but before departing Shachath notices that Eunice is watching her. The fact that the nun could lay her eyes on such an entity is an immediate telling sign that she is no mere mortal. The two exchange words with the possessed Sister looking very nervous and frustrated with the host's presence in the asylum. Shachath makes it clear that she can see through the demon's disguise and can see that the real Mary is begging for death and an end to her torment, at this remark the real Sister Mary Eunice breaks free of the demon's control and begs the Angel to release her, but she is quickly silenced by the impatient demon. Shachath promises they will meet again and leaves.
With the only real threat to her now gone Eunice continues her wrath among the asylum and begins placing her pawns where she needs them. She confronts Dr. Arden, who has grown more and more despaired over Mary Eunice's loss of innocence, to convince him to give her his loyalties. She promises that she got rid of his threat, Sister Jude, but has kept some pieces of evidence for herself if he dares to reject her offer of partnership. In a battle of dominance Arden attempts to slap Eunice, but she makes a display of her power and simply tosses him across the room without lifting a finger. Arden is effectively subdued.
Arden meets Jude at a church, seemingly with his tail between his legs, and in contriteness tells her that he is struggling with what is at works within Sister Mary and admits that he believes something otherworldly could be at foot. Sister Jude reluctantly obliges to helping Arden subdue Eunice.
Jude waits in Mary Eunice's office with the intent to kill her under the pretense that she's actually there to discuss matters with the sister. Instead, however, Eunice locks Jude in with Leigh Emerson. The resulting altercation almost ends Jude's life.  Sister Jude ends up constrained to a bed and drugged as the Monsignor reminds her of all that has transpired including her attempt to murder Leigh and her actual murder of Frank McCann, who in reality was murdered by Eunice with the intent to frame it on Jude. Sister Jude, because of her alleged actions and the real actions of Sister Mary Eunice, is now a permanent inmate at the Briarcliff Sanitarium.
After Lana's struggle with Thredson in his basement, she escapes only to be involved in a car accident that has her waking back in Briarcliff. Sister Mary Eunice tries to console her and implies that she will look into Lana's story involving Thredson. This, of course, is a lie. Sister Mary Eunice reveals to Lana that she is pregnant with Thredson's baby and after Lana performs an abortion on herself with a hanger, thinking she succeeded, Sister Mary Eunice, using her power of insight, reassures her that she is indeed still pregnant. To add insult to injury she then hires Thredson as the asylum's psychologist.
Monsignor, now equipped with a revelation given to him by Shachath, finds himself being attended to by Mary Eunice after he was crucified by Leigh. In a desperate attempt to exorcise the sister, the monsignor lunges at Eunice and places his rosary on her forehead and begins to recite a prayer. Mary Eunice brushes him off sending him flying back to the bed on which he was laying with his arms stretched out and body held in place by some unseen power. She tempts and teases him as she mounts him and eventually rapes him. Keep in mind that this does not only take something valuable from the Monsignor, but also from human Mary Eunice. She taunts him over his virginity and his body's clear interest in her despite his minds rejection of the despicable act taking place. Mary notices Dr. Arden witnessing from the doorway.
After being raped, the Monsignor Timothy Howard consults with Sister Jude, whose sanity is clearly slipping after Mary ordered she be administered electroshock therapy, in a moment of clarity on her part she tells him to kill her.
Sister Mary Eunice later visits Dr. Arden, who is bringing food to the Raspers, and she suggests lobotomizing Judy, to which Dr. Arden flatly declines. Now despondent over being mocked by the aliens and losing the purity of Sister Mary, he executes the Raspers before attempting, and failing, to kill himself, then begging for Sister Mary to give him some form of mercy. Disappointed at Arden's loss of dignity and desperation, Sister Mary leaves him in the forest.
Again Timothy is confronted by Sister Mary Eunice in the midst of his prayer. She offers her body to him again, he rejects it, she exploits his inner ambitions by hinting to him her grand scale plan involving the Vatican and him as pope, again he rejects the idea. She then taunts him over his obvious desire to kill her and toys with the many ways he could go about taking her life, even revealing that he could use his rosary like he did on Shelly, demonstrating again her ability to know all secrets hidden in her victims mind.
Sister Mary Eunice finishes by reminding the Monsignor that he is weak and after what she did to him she owns him, body and soul. To this, he rebuts that she, in fact, does not own him and that he will cast her out. He reminds the demon that he can still sense the true Mary Eunice and will free her. Enraged, the demon corners Timothy on the stairway and grips him by his shoulders, promising to not only omit the Monsignor from its plans but to devour the very last morsel of soul that is left of Mary. At this, the real Mary breaks free and cries to the Monsignor that she is tired and, in effect, cannot keep fighting for control over her body, she wants to let go. Timothy tells her to then let him go, she does, and swiftly and without hesitation, he grabs Sister Mary Eunice and tosses her over the landing of the staircase, and she falls to her death.
Shachath appears before Sister Mary Eunice as she lays dying. Eunice asks the Angel to take her, Shachath replies "I will take both of you", ending the demon's reign over the sanitarium. Her body is later cremated by Dr. Arden. Still lost in his obsession with her and now completely void of hope or reason to continue living, Arden lays atop her body as is pulled into the furnace where he burns alive along with her corpse.
In 1962, Sister Mary Eunice is sitting behind her desk filing paperwork for Pepper. She converses with Pepper's sister to find out the reason why she is being admitted. She tells Sister Mary Eunice that Pepper sliced off her baby's ears and drowned it(although pepper was framed for the murder by her sister and her husband). Sister Mary Eunice is horrified by this but Later Sister Mary Eunice senses remorse in pepper and makes Pepper an assistant in the library to reorganize magazines and articles, there Pepper finds Elsa has made the front of a magazine showing she finally became famous.
Powers and Abilities
Upon being possessed by the demon, Sister Mary developed some of its power.
- Telekinesis: The Demon, while in Sister Mary's body, can use its mind to move objects and people without touching them.
- Clairvoyance: While being possessed by the Demon, Sister Mary can enter into the minds of others, read their thoughts, and access their memories, granting her an inherent knowledge of others' past sins, regrets, and moral choices.
- Concilium: The Demon, while in Sister Mary's body, can influence the minds of others through seduction and persuasion.
- Transmutation (presumably): While being possessed by the Demon, Sister Mary can instantaneously travel from one point to another.
- To Monsignor: "Good one, Father. You wanna hear mine? There was a priest, the dirty beast, whose name was Alexander. His mighty dick was inches thick: he called it `salamander’."
- To Sister Jude: "I've taken the liberty of choosing one, Sister Jude. A cane befitting their... transgression."
- To Pepper: "You are my special project. No filthy toilet scrubbing."
- Sr. Mary Eunice: "We're all going to be together in the dark watching The Sign Of The Cross, a movie full of fire, sex and the death of Christians. What fun!"
- Sr. Mary Eunice: "I know everything. I'm the devil."
- To Lana: "She's not harmless; she drowned her sister's baby and sliced his ears off."
- To Lana: "Sr. Jude calls this her stairway to Heaven."
- To Sister Jude: "It's not big enough Sister. Punish me, Sister, please! I'm so weak and stupid! Stupid! Stupid! Stupid!"
- To Dr. Arthur Arden: "No, I really shouldn't. Sr. Jude said sweets lead to sin."
- To Lana: "Most of the babies... they are born a little cuckoo"
- To Shachath: "Oh, heavenly host! Will you release me? Can you release me? Oh, shut up, you stupid sow! ... She likes it here... we like it... and we have work left to do."
- To Shachath: "Take me..."
- To Dr. Arthur Arden: "Please doctor you must tell me... What are these creatures?"
- To Pepper: "Is that redemption I see?"
- Sister Mary Eunice is one of the main villains/antagonists of Asylum along with Oliver Thredson being the second
- The devil's main goal was to rise up in the hierarchy of the church and overthrow it and Sister Mary Eunice was the key to that but failed due to identity exposure.
- She is the second character to be portrayed by Lily Rabe. The first was Nora Montgomery, the third is Misty Day, the fourth is Aileen Wuornos, and the fifth is Shelby Miller.
- Sister Mary Eunice has been absent in three episodes overall throughout the second season. Those episodes are Spilt Milk, Continuum and Madness Ends. In all of these, the cause was her confirmed death in The Name Game.
- Sister Mary Eunice is the second American Horror Story character to make a crossover appearance in another season.
- She reappeared on December 17, 2014, Freak Show Mid-Season Finale.
- Sister Mary Eunice is the second key character linked, next to Pepper, that shows that Season 4: Freak Show is in fact connected to Season 2's: Asylum.
- Not many were aware of her possession besides Sister Jude, Timothy Howard, Arthur Arden, Shachath and The Mexican.
- See also: Sister Mary Eunice/Media
- ↑ Episode: Welcome to Briarcliff
- ↑ Episode: Tricks and Treats
- ↑ Episode: Nor'easter
- ↑ Episode: I Am Anne Frank: Part 1
- ↑ Episode: The Name Game
- ↑ Episode: Dark Cousin
- ↑ Episode: Unholy Night