- "Guilty and innocent aren't our business, Mox. Killing who we're paid to IS our business."
- ―Millie, to Moxxie
Millie is a short Imp with a long demonic tail and white markings. She has red skin, eyes with yellow scleras and black pupils, and long black eyelashes that extend beyond the sides of her hair.
Similar to her mother, she has two black horns with three thin white stripes and greyish-black hair worn in a messy bob style and bangs that cover half of her right horn. She has a beauty mark on her left cheek and a gap between her front teeth.
Millie's head is noticeably more human-like (although still without a nose) than a lot of other imps, lacking the pointed upper lip. Her teeth also usually appear flatter than the sharp conical teeth most demons have.
Her usual attire consists of black lipstick, a simple black choker, a cold-shoulder black crop top with gold buttons where the straps at the top meet the torso piece, torn black pants, fingerless black gloves, and black footwear that does not cover her hoof-like toes. During the episode Loo Loo Land, she wears sunglasses, a black suit and tie with a white shirt while guarding Stolas, just like Blitzo and Moxxie.
Millie also has a black tattoo in the shape of a heart on her left shoulder, and two white splotches on the insides and outsides of each of her elbows.
In the pilot, her hair had a white splotch mark near her left horn, although it was removed by the series proper.
Millie is very lively and cheerful. Often with a smile on her face and rarely standing still, she is a clear extrovert and isn't afraid to speak her mind. This is regardless whether it's expressing her excitement or flipping off a coworker.
Also, as Millie is the bruiser of Blitzo's employees and seems to enjoy her job, it can be assumed she's tough and very violent as well. This is highlighted during a conversation Millie had with her mother and sister. According to Moxxie, she is aggressive in "the sack" as well as her job. In "Murder Family", she appeared to be very unsympathetic about killing a family, only caring if it was what the client wanted, showcasing her dedication to her work. Despite this, she cares very much about her husband and apparently her family. She has a childlike fondness of Loo Loo Land, triggered by familial memories of going there as a child and gets easily excited by all the merchandise. She can get very jealous too like when she couldn't participate in the Harvest Festival games.
In "Spring Broken" and "The Harvest Moon Festival", Millie is shown to turn quite vicious whenever someone harms Moxxie, to the point of going nearly feral in the latter episode. In said latter episode, she is also shown to be a bit defensive of her work seeming quite annoyed when someone implies that freelance work doesn't pay well. As mentioned before, Millie's violence streak often gets her carried away with her killing to the point of mindlessly attacking and letting her rage get the best of her. This was also showcased by her trying to defend herself against her mother’s scoldings, claiming she was “seeing red” when she fought Striker.
- Fire Resistance: TBA
- Weapon Proficiency: Millie is skilled at using a giant battle axe to slice up targets, as shown when she eliminated several D.H.O.R.K.S. agents with her axe in I.M.P.'s standoff at D.H.O.R.K.S. headquarters. Like her husband, she's also adept at using firearms, and she can also create makeshift weapons on the fly, such as when she made a Molotov cocktail to throw at the Catfish Monster.
- Closed Combat: Millie is adept at closed combat. She has the leg strength to twist and snap a target's neck in between her thighs, as demonstrated on a D.H.O.R.K.S. agent.
- Millie speaks with a Southern accent.
- Viv has stated that she would change Millie's voice actor once the actual series premieres but would still keep her previous voice actor, Erica Lindbeck, to voice Loona. Later, actress and dancer, Vivian Nixon, was hired to voice Millie.
- In Vivziepop's 2019 short Holidaze as an ornament on a Christmas Tree, there is a tree carved with initials "M+M →B←" in a heart that alludes to her, Moxxie, and Blitzo.
- While Millie seems to tolerate Blitzo's intrusions, she is not shown to be comfortable with other men flirting, as the game attendant pushing Moxxie away and attempting to flirt with her noticeably upsets her.
- In "The Harvest Moon Festival", it revealed that she is no longer allowed to participate in the Pain Games because she was responsible for nine out of the fifteen funerals that occurred at the time.
- It is also revealed that one of her brothers got married at one point and that she got severely injured while competing over who would catch the bouquet but in the end Millie managed to do so.
- In "Truth Seekers", she claims she is about five years older than Loona. If this is true, this places her and possibly Moxxie's age somewhere in her mid or late 20s.
- According to Blitzo, Millie is strong to the point (especially when she’s upset) it would take a “roided-up” hippo to take her down.
|Hazbin Hotel||Helluva Boss|
|Main characters||Charlie Magne • Vaggie • Angel Dust • Alastor • Husk • Niffty||Blitzo • Millie • Moxxie • Loona|
|Supporting characters||Cherri Bomb • Fat Nuggets • Sir Pentious • The Egg Bois • Razzle and Dazzle • Katie Killjoy • Tom Trench||Stolas • Agent One • Agent Two • Cletus • Collin • Keenie • Octavia • Robo Fizz • Verosika Mayday • Wally Wackford • Striker|
|Minor Characters||Crymini • Exorcists • Helsa von Eldritch • Lilith Magne • Lucifer Magne • Mimzy • Travis||Barbie Wire • Catfish Monster • Eddie • Joe • Lin • Loo Loo • Loopty Goopty • Lyle Lipton • Martha • Mrs. Mayberry • Ralphie • Sallie May • Stella • Verosika's crew • Vortex|
|Overlords||Alastor • Rosie • Valentino • Velvet • Vox|
|Other Characters||Arackniss • Baxter • "Henroin" • Molly • Seviathan von Eldritch||Fizzarolli • Tilla • Mammon|