|Real world information|
|First appearance||"Meet the Reaper"|
|Voice actor||Grey DeLisle|
Mandy is a 12-year-old girl who typically has a cynical and arrogant attitude and is the main deuterogamist. Unlike Billy, she is more stable, sane, and intelligent.
Mandy is a morbid little girl with blonde hair that is shaped distinctively like devil horns and for some reason, she has no nose (except two very small nostrils), which characters in the show remarked about more than once.
Her outfit consists of a small, pink dress with a flower in the center, black shoes and a black headband.
Mandy seeks world domination, but when it gets offered to her, she turns it down, because she either wants to do it herself or wait for the right moment. She is incredibly intelligent and will stand up to anyone or anything, which is why she always gets her way.
She hardly ever smiles or has a neutral expression, and it seems she had a frown on her face even before birth. Next to never being pleased by anything, she never smiles because her smile seems to cause the whole universe to implode simply because Mandy smiling is an unnatural occurrence that the universe can't seem to handle, as shown in the episode "My Fair Mandy."
She is sworn enemies with the popular school girl, Mindy.
Mandy bosses Grim around constantly and makes him do her chores; she often does the same to Billy as well. According to Billy, she's afraid of professional figure skaters, but she denies this and simply says, "I just don't trust the way they spin is all." In "Billy and Mandy's Big Boogey Adventure," her worst nightmare is revealed to be getting old, fat, nice and being married to Irwin.
Unlike Billy, Mandy is rarely responsible for the adventures/troubles the trio often has. In fact, she's usually right there trying to prevent him from causing more mayhem or simply to solve the problem. Though her "concern" never lasts long; and when it gets out of hand, she just ends up leaving the scene or stop bothering.
It was shown in "Billy and Mandy's Big Boogey Adventure" that she may have hidden feelings for Billy; as she seemed extremely saddened with near tears in her eyes when thinking he died, and was delightfully surprised when he was shown to be unharmed. She said once, in an effort to help him in "The Bubble with Billy," she says "Billy, we've known each other now for what seems like a nightmarish eternity.... and though I insult and lie to you daily, steal your stuff, make fun of you, your family, or anyone that looks like you, I still don't feel like I.......... know you.........."
It has been said that they love each other, though they do not know it yet.
Nevertheless, they do have a certain relationship, with Billy sometimes calling her "My dear, sweet Mandy." In the episode "Keeper of the Reaper," he says "I'll miss your hands on approach to life." Mandy nearly always pushes Grim to help Billy saying many excuses to help or save Billy, despite Grim insisting to leave the boy. In "Which Came First?" when Mandy pushed Grim into saving Billy, he said, "Awww... I knew you two were sweethearts," and then he proceeded to make kissing noises. She then punched him and makes an excuse that Billy owes her $5.00. Also, in the episode "Puddle Jumping," after Billy disappeared into a "cosmic sink hole" that magically appeared in the bottom of his kiddy pool due to a beam of sun light reflecting off Grim's scythe and shinning into the pool's bottom, Mandy insisted that she and Grim go after him and bring him back, claiming that he was her “science project,” even though Grim really wasn’t up much for the rescue. She has also allowed Billy to have physical contact with her, something she usually doesn't accept from others.
- Pink dress with a centered flower (yellow petals and blue stamen/pistol)
- Black Mary Janes shoes
- White socks (unknown length)
- Pale skin (almost white when compared to other humans, and on par with Velma Green's)
- Black headband
- Blonde hair styled in what are classified as devil horns, but can be confused for a crescent moon shape (AKA, a "C" or backwards "C")
- No nose (though nostrils are present when sniffing and in close-ups)
- Basic large eyes with no real color defined (though dark brown, green, and blue are viable suggestions)
- Muscularly superior to all she comes in contact with (everyone)
- Publicly calm and quiet
- Mentally unstable (angry, lustful, rarely shown, questionable schizophrenia; among other illnesses)
- Paranoid (not to Mandy's caring or attention in most situations)
- Completely irrational fearfulness (ice skaters)
- Anger driven and manipulated by negative emotions
- Controlling; demanding
- Persevering (strives to do as she commands to the very end, albeit, such intentions are usually quite harmful to others)
- Overall intelligent for her age, or in general. She even understands complex functions of adult life, such as finances and governmental manipulation of holidays.
- Mandy is the only character to officially not have a designated nose, though nostrils are present when in close-ups.
- She is one of the most sensible and intelligent characters.
- Though the dialogue of the show always says, "Mandy never smiles," it is seen that she often does in very brief intervals that aren't visible without a good attentiveness or being able to go through each frame of an episode. Also, she smiles in the first few episodes of the series.
- Mandy has almost exactly the same traits of Gaz from Invader Zim, along with her attitude and disposition.
- In the future of Billy's wedding, Mandy wears glasses and looks like her teacher, Mrs. Butterbean.
- During the first few seasons of the show, some fans thought that Mandy was Billy's sister. This is made fun of in the show when Billy's dad said that he thought Mandy was his daughter.
- According to her father, a pack of wolves tried to raise her as one of their own when she was born.
- Mandy seems to care for Billy in some episodes, though it might be because he can take the insults she fires at him, and nobody else can.
- Her smile has the ability to warp reality (but since she almost never smiles, no one can be sure if it happens every time, or was just a one-off occurrence), she has superior physical strength and fighting skills to fight just about everyone (including all monsters, who should be far stronger than even the best of the best humans), and the ability to control the minds of every character in the series (except Grim).
- Even thought she has no nose in the show, in FusionFall, she has a nose.