Serleena is an extremely evil alien who will kill without mercy. She is known to insult her allies and enemies alike, constantly telling them how pathetically useless they are. She usually prefers to eat anyone who stands in her way, though killing them by other means, such as using her tentacles, tends to be favourable as well.
As the evil leader of the Kylothians, Serleena was initially drawn to Earth several years back when the Zarthans attempted to bring the Light of Zartha to Earth under the watch of the MIB agency. Upon entering the scene, Serleena kills a Zarthan leader and dispaired as what she though was the Light of Zartha, flew into orbit. Over the years she travelled from planet to planet in her search for the shuttle, constantly being disappointed and destroying many worlds in bitter anger. However, she was contacted by Scrad/Charlie who notified her that the light had been back on Earth the whole time. After a quick change of course, Serleena headed to Earth, landing in New York.
Slipping through the gardens in the form of the serpent, she slithers across the ground, coming across a magazine. Wind blows the pages open to an ad for Victoria's Secret, where the female model Lara Flynn Boyle wears black lingerie. The head opens wide and then hundreds of serpents come out, screeching and shrieking, forming herself into exact copy of lingerie model from the magazine ad. Immediately after Serleena fully forms, a rapist dressed in leather grabs her and holds a knife to her neck. He licks her and tells her that she tastes good, and then drags her to a nearby bush. Hidden from view, Serleena roars and eats the man, his legs visible as she eats him upside down. She walks back from the bush, licking her fingers and moving her stomach from side to side. Suddenly, she stops and then looks at the ad again. Understanding that her big stomach is ruining her human form, she growls and then walks back to the bush and vomits the rapist. She is coming out from bush with her slim stomach again, carrying rapist's clothing and walks with it through the alley of Central Park.
She first stops by Scrad/Charlie´s department to find him watching TV and eating junk food. Without him knowing she´s Serleena, Scrad/Charlie gets impressed by her beauty, only to have her shove two tentacles into their ears as a bitter reminder of who they were talking to. They talk about finding the light and agree to look for information at a pizzaria nearby while she eats a greasy hamburger.
At the pizzaria, Serleena questions an alien who might know the where-abouts of the Light; getting no usefull information, she slices him with her tentacles. She then storms MIB headquarters, taking everybody captive and releasing the agency's convicts for some assistance. She then sends a handfull of these convicts after Jay as he attempts to restore Kay's memory. After a quck memory restoration and brief brawl, Kay and Jay discover the Light is actually Laura Vasquez, a worker at the pizzeria and daughter of Zarthan Queen Laurana.
Upon returning to headquarters Jay stops the countdown of a machine that would launch Laura into space, and shoots Serleena before she can eat Kay. She is seemingly destroyed, but her initial worm form survives. Quickly, she regenerates and steals a futuristic vehicle to chase after the trio of Jay, Laura, and Kay. After an intense chase scene Serleena is tricked into being eaten by the giant worm, Jeff, along with her spaceship.
Thought to be safe from Serleena's wrath, the trio reach a rooftop and prepare a hidden shuttle for Laura to leave on. However, Jeff bursts through the roof and explodes, revealing Serleena in a giant mutated wormlike form. As Jay was thrown around by her tentacles, trying not to be eaten, Kay casually spoke with Laura before shooting Serleena, releasing Jay. After launching Laura, Serleena returned and showed her true form, that of a huge viney plant, and flew after Laura, but Jay and Kay casually shot her with their weapons, destroying her in a bright fireworks display and returning to HQ.
- In Men in Black: Alien Crisis a simulation of her plant form is used as a boss fight during initiation.
- In the Men in Black III App, Serleena appears in her plant form as a boss.
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