Mantha has blue-green tinted skin typical of a corpse. Her hair is blue with darker streaks, and it falls between mid-back to waist length. She has almond-shaped purple eyes. She wears casual and torn clothing. Her regular outfit consists on a pink shirt with a white flower on it and a short faded black shirt underneath, tattered purple flare pants and black and pink sneakers.
In the movie, her appearance is generally the same. There are a few minor differences - her shirt has a yellow rose instead of the white-petaled flower, her shoes are solid black, and her eyes have a slight glow to them.
Mantha is fiercely independent, often considering accepting help from others as a sign of weakness. She takes great pride in her independence and ability to make rational decisions without the influence of others. She values rationality and political correctness, and frequently tries to instill the belief that all creatures are equal into her classmates.
Mantha greatly dislikes the stereotype that zombies are unintelligent and slow, as she is neither of those things and goes out of her way to defy the common perception of her kind. Mantha can be very sensitive about the subject, as it angers her quickly.
Mantha appears to be more benign that many of her classmates. She is willing to befriend others, such as Casper, Ra, and Jimmy, though she still values being monstrous. She also advocates for the equal treatment of all creatures in the Underworld, and is usually willing to help others in the case that problems should arise.
Mantha can also be condescending, sarcastic, and cynical. She doesn't take well to being ignored, and her adamant nature sometimes prevents her from seeking help when she needs it.
Mantha is able to remove parts of her body at will, despite lacking any physical connection between her head and those parts of her body removed in this fashion, Mantha remains able to control said parts at all times (e.g., she is able to see using eyes removed from their sockets and detached from their optic nerves). This "ability" is sometimes a hindrance i.e. she is often unable to keep them attached to her body. She is also able to lend her body parts to those who can use them e.g. in The Last Dance she gives her legs to Hedy Hopper so she could dance with Frankengymteacher in order to remove the dancing shoes stuck to her feet.
Mantha's parents have only been referred to offhandedly on one occasion in the first season. It is unknown what they look like or who they are. In Time Waits for No Ghost, it is revealed that they live in a mausoleum. The second season episode Stage Fright showed two similarly tinted arms and eyes alongside a camera - possibly intended to represent her parents. Otherwise, there is no explicit references to them outside of this instances.
In season two, a previously unheard of character by the name of Frankie was introduced. He was apparently a pen-pal of Mantha's, and it was revealed that she harbored romantic feelings for him. When he arrived at the dance, it was revealed that the feeling was mutual. However, aside from this episode, Mantha never mentions him in any episode before or after this one.
Ra, along with Casper, is Mantha's best creature friend. Like with Casper, Mantha sometimes has to look out for Ra due to his naiveness.
Jimmy and Mantha are good friends, although Mantha can sometimes get upset when Casper hangs out with Jimmy rather than with her and Ra.
When she isn't with her gang, Dummy Girl still acts hostile towards Mantha. However, Dummy Girl was impressed when Mantha confessed that she had Crypt Critters and decided to go to the Nurse and asked Mantha is she was okay.
- In the comics, Mantha's skin is light blue instead of light green/teal.
- Mantha is one of the most popular female characters of the Casper's Scare School fandom, along with Dummy Girl.
- In the movie, Mantha had a yellow rose in her shirt. Yellow roses are typically used to symbolize friendship.
- Her name may be a shortened version of the popular name "Samantha", though this is never confirmed within the series.
- Mantha makes several references to the fact that she is reanimated corpse, implying that she had been a living human at some point before her reanimation. The fact that her permanent residence is a mausoleum reinforces this. This makes her one of the three characters that are confirmed to have lived as a human before becoming a monster - the other two being Ra and Fly Boy .
- Mantha is held together by surgical sutures. This was revealed in the episode Paramedic Paranormal.
- Mantha can play the drums very well, as shown in the season one episode Bands on the Run.
- Mantha's age is never addressed or referenced in the series, making her true age unknown.
- In season two, it is revealed that Mantha is a princess, though this is something she apparently had no prior knowledge of. It is unsure what political standing she holds in the Underworld, or whether or not she held this title in life or acquired it after death. This makes her and Ra both undead royalty.