Mas is a defective, however Mas is still an extremely intelligent Irken, though she is also very immature. Her immaturity caused her to be sent to Earth after a (seemingly) harmless prank on the Tallest. In the prank, she had set up fireworks at precise angles so when fired, they would just barely miss the Tallest's heads. The Tallest then sent her to Earth as a punishment, but also in hopes that her immaturity would destroy Zim. Upon arriving at Earth and meeting Zim and GIR, Mas decided she needed a robot, and so she created a SIR unit based on how GIR looked, and, trusting Zim's belief that GIR is the most advanced in SIR unit technology, created hardware that matched that of an actual SIR, naming it SIRA, the A meaning Advanced. While she is currently on Earth, she is merely waiting there until the Almighty have chosen a planet for her to try and conquer on her own, for right now she is under strict orders to let the Earth-conquering stay Zim's mission. She is 150 Irken years, approximate to just under 15 Earth years, however she blends perfectly with the kids in Mrs. Bitters Skool class.
As an Irken, Mas has lime green-ish skin, unusual golden eyes and PAK, and wears a variant of the standard Invader Uniform. Instead, she wears a red crop-top with a variant of the Invader symbol on it, a red skirt, gold leggings, black boots, and golden shoulder pieces and neck piece. In disguise, she wears a blue version of the typical Irken uniform. She also wears a bracelet that makes her skin appear human-like, and makes her eyes appear human. She will also wear prosthetic ears and a nose to hide the lack thereof, and wears a curly, brown-haired wig to hide her antennae.
Zim: Mas has a crush on Zim, though it is well hidden and only SIRA knows. It is unknown, however, if Zim returns the feelings.
GIR: Mas enjoys playing games with GIR and SIRA, and loves the fact that he's immature, quite like her.
SIRA: Mas and SIRA are like sisters, and SIRA, through whatever personality mode she is in, will do anything to protect Mas, and vice versa.
The Almighty Tallest: The Tallest don't particularly care for her after the firework prank, but they seem to have forgiven her, as she sent them a Voot Cruiser full of snacks a day for a month after landing on Earth.
Dib: Mas and Dib's friendship abruptly ended when he overheard a conversation between Zim and Mas when Mas told Zim she was Irken. However, neither one tries to kill the other directly.
Gaz: The play video games together in the arcade. Gaz considers Mas a good friend, but bad competition.