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. With the exception of Zed because she clearly has a crush on him. 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 favorable 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 despaired as what she though was the Light of Zartha, flew into orbit. Over the years she traveled 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 is on the page. She then proceeds to transform into an exact copy of the woman in the picture, and moments after she is finished, she is attacked by a mugger named Creepy, who drags her behind a bush with the intent of raping her. He is instead eaten by Serleena however, and she returns to the magazine with a full stomach. Realising that eating a human ruins her disguise, she regurgitates his remains before his clothes can be digested, taking them to change into.
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 Lauranna.
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 (with Kay alluding to this, although Serleena arrogantly assumed that Kay was going to deliver the killing blow until he corrected her), also telling her that her flight is canceled, referring to her plan of sending Laura via a spaceship to Kyloth. 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 viny 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.
- Serleena is similar to Mother Brain and Ganondorf from the Metroid and Legend of Zelda franchises, respectively: Each of them desire to acquire a great power source or weapon and use it conquer the world, and in some cases, the whole universe.
- Serleena is also very similar to Lord Voldemort from the Harry Potter series, Hopper from A Bug's Life, and Ursula from The Little Mermaid: Serleena, Voldemort, and Hopper are all ruthless and tyrannical leaders who show little to no mercy to their henchmen and/or enemies, and like Ursula and Voldemort, Serleena is a very intelligent and powerful shape-shifter.
- Famke Janssen was originally cast as Serleena and had even filmed some scenes, but was forced to drop out of the project due to a death in her family.
- Halle Berry, Jennifer Lopez, and Yeardley Smith auditioned for Serleena.
- Serleena's goals are very similar to Edgar the Bug's from the first movie.