She previously attended St. Olga's Reform School for Wayward Princesses because of her rambunctious behavior. After headmistress Miss Heinous and her faculty were overthrown and driven out of the school in the episode "St. Olga's Reform School for Wayward Princesses", Pony Head helped turn the reform school into a party location.
Pony Head is literally the head and neck of a unicorn without a body. She has light blue fur, a pink mane (which constantly flows and flutters), teal eyes with gold stars for pupils, and a teal, striped horn. On each side of her neck, there is a pink heart. Sparkles and glitter tend to fall out of the bottom of her neck, though this no longer happens following the destruction of magic.
Pony Head's most prominent character trait is being a party girl; she loves partying and dancing, sometimes getting carried away with it, as shown in "Party With a Pony". She can be quite bold and rash, as well as sarcastic and laid-back. She can also be quite competitive, as seen when she played video games with Marco, and she can be rude and underhanded. She is also quite egotistical, as seen in "Sleepover", where she cites "Pony Head color" as her favorite color and that she has a crush on herself, and in "The Ponyhead Show!", where she makes her self-titled show all about herself and disregards her guests and fellow segment hosts.
Despite this, Pony Head is loyal to her friends and willing to endanger herself to help them. She is quite possessive, initially trying to get rid of Marco so she could have Star all to herself, as well as a compulsive liar, frequently stretching truths to gain what she wants. Pony Head also has a tendency of being overdramatic, such as her reaction to the Bounce Lounge closing in "The Bounce Lounge", her interactions with her sisters in "Ponymonium", and the lengths she goes to watch her favorite Korean drama in "Bam Ui Pati!"
Pony Head has been best friends with Star since they were kids and loves it when they get to have fun together. However, she is very possessive of their friendship and is upset by Star also calling Marco her best friend. Star's disappointment in Pony Head lying to her about ditching Marco leads Pony Head to give her pair of dimensional scissors to Star and bravely sacrifice herself, facing the guards to save Marco.
Pony Head is such close friends with Star that she is willing to drop whatever she is doing and rush to Star's aid if she is in trouble, as demonstrated in "Starcrushed". In "Scent of a Hoodie", she helps Star get over missing Marco and obsessing over his hoodie. In "Ponymonium", Pony Head is shown to be such close friends with Star that she considers Star to be her sister. In "Bam Ui Pati!", she calls Star her "favorite sister", and allows her to attach her replacement horn to her forehead.
After finding out that Marco is Star's other best friend, Pony Head gets jealous and threatens him to not get between her and Star. She calls him "earth turd", tries to push him off the dance cloud in the Bounce Lounge, and ditches him at the Amethyst Arcade. However, once she realizes how important he is to Star, she goes back to save him from the guards. Her heroism puts her on good terms with Marco, and when she departs for St. O's, she appreciates him telling her good luck and calls him by his real name. Though she still insists on being known as Star's "best bestie", she remains on good terms with Marco when next they meet.
In "Goblin Dogs", Pony Head tries to monopolize Star's attention, making Marco interact with her friend Kelly. Despite this, she still treats Marco quite well, even addressing him by name throughout the adventure (except in one instance).
In "Sleepover", she has no problem with having Marco join in on the sleepover game, and even teases him lightheartedly over his crush on Jackie Lynn Thomas. In "Pizza Thing", Marco is still a little annoyed by Pony Head's wild behavior, but the two manage to cooperate in the end to bake a pizza together.
In "The Bounce Lounge", Pony Head expresses irritation toward Marco when he tells her and Star to accept the Bounce Lounge's closing and denies Marco even saying it when Milly Sparkles says the same thing later.
She is unfazed when Star's crush on Marco is revealed in "Starcrushed", claiming to have been aware of it for some time.
In "Monster Bash", Pony Head is shown to still hold a rivalry with Marco, smugly bragging to him when Star calls her "the best". In "Stump Day", she admonishes Marco for throwing Star a birthday party without asking her, claiming he has a need to "control every situation like a maniac". When the Stump has them in its grip, she apologizes for the way she acted towards him, but at the same time claims that her "thoughtful criticism" has helped him improve as a person. In "Divide", she continues to call him "Earth Turd", but she goes along with his plan to stop Meteora.
Pony Head has twelve younger sisters, with whom her relationship is considerably hectic. She frequently argues with them, defends herself against their plots to depose her claim to the Cloud Kingdom throne, and describes them to Star as "totally insane". Nevertheless, she later says that's just how sisters act toward each other and that she still loves them, becoming furious at Star for calling them as such. She later cooperates with them to improve Eclipsa Butterfly's popularity among Mewmans in "The Ponyhead Show!" and "Queen-Napped", though she frames them for Eclipsa's kidnapping in the latter episode.
Pony Head and Tom do not interact much with each other, but they seem to be on relatively good terms. Despite this, Pony Head seems to disapprove of Star's relationship with Tom, as shown in "Club Snubbed", where she tells Star to not fall for Tom's apparent shunning; in "Demoncism", where she complains after seeing them holding hands; and "Cleaved", where she intentionally does not tell Star that Tom was looking for her.
- Multipurpose horn: Pony Head can shoot laser beams from her horn or use it similarly to an electric drill.
- Levitation: Pony Head can levitate or fly at high speeds. In "Sleepover", she is strong enough to carry several people at once (though with great difficulty). She still possesses this ability after the destruction of magic in "Cleaved", proving that it is a biological function rather than magical.
- Magic: In "Pizza Thing", Pony Head uses her horn to magically restore a crushed car and command it to drive itself back to its owner.
- Telekinesis: Pony Head can manipulate items through thought, as this is how she uses her phone without having limbs.
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- Pony Head is based off previous artwork by Daron Nefcy.
- In early concepts, Daron Nefcy wanted Pony Head's design to look like she was "drooling, and blood dripping out of the neck – but then really sparkly and really big eyes".
- She can wreck an entire dimension consisting of video game consoles using only her ability to shoot laser beams out of her horn.
- "Goblin Dogs" reveals that she can store things inside her neck.
- In "Sleepover", Pony Head reveals that she doesn't have a stomach. She also admits to having a crush on herself.
- In "Running with Scissors", Pony Head reveals that she stole the dimensional scissors she ended up giving Star from Hekapoo the Scissors Enforcer.
- "The Bounce Lounge" reveals that Pony Head cries rainbows.
- According to Star and Marco's Guide to Mastering Every Dimension, Pony Head's real name is Lilacia (which she hates being called), and she's the oldest of thirteen sisters.
- "Demoncism" implies that Pony Head has had several boyfriends in the past; When she mentions that one of her ex-boyfriends went through the titular procedure, Star asks "which one?
- According to Pony Head's ID in "Bam Ui Pati!", her birth date is August 4, 2001.
- From "Bam Ui Pati!" onward, Pony Head's horn is an artificial 3D-printed horn, created to replace the one Meteora Butterfly broke off in "Skooled!"
- In "Sad Teen Hotline", it is revealed that Pony Head has a habit of staying up until 4:00am.
- Sometimes spelled one word as "Ponyhead".