Queen of Earth's volcanoes. Lava Girl is one of the superheroes Max creates in his dreams. She is another superhero who protects Planet Drool. Her powers include general thermal manipulation, production of light, and shooting lava out of her hands. She is an ally and friend of Shark Boy. At first she thinks that she is evil and destroys everything she touches but she later learns that she is the light needed to defeat the darkness.
Lava Girl possesses a very sweet and kind nature. However, much like Shark Boy, when angered, her temper (and temperature) can flare up to dangerous levels, making her a danger to others arround her. Her temper can be so fearsome that she can cause Shark Boy to cower in fear.
Lava Girl was at some point created and brought into reality by Max's dreams. She apparently began life in Planet Drool's volcanos. At an undisclosed point, she met with Shark Boy, and the two became allies, later forming a close (if competitive and bickering-filled) friendship. When Linus's power-lust and Mr. Electric's ambition threatened to plunge Drool into darkness, she and Shark Boy were quick to travel to earth, where they rescued their creator from a powerful electric storm. Once on Drool, she and Shark Boy assisted the seemingly powerless max in attempting to set things right on the dream-planet. The three started at Mt. Neverrest, where they briefly confronted Mr. Electric. Lava Girl defeated several plugs in battle and briefly stunned Mr. Electric, but all three were captured and dumped into the realm of Forgotten Dreams.
In the Realm of Forgotten Dreams, the trio meet Tobor, who dispenses personal wisdom to each, which briefly dispels Lava Girls doubts about her purpose and morality. She then travels with the other two to the Train of Though aboard Tobor's disembodied facial features, where she, along with everyone else, is horrified to discover that the train is on a crash course. She is the first to bail out, and all three land in the Land of Milk And Cookies atop a massive cookie floating on.... Well, a stream of milk. Just in time to watch the Train crash. She notes the setting, then urges Max to dream, singing an off-tune lullaby and cautioning Shark Boy to treat Max more kindly, accidentally burning the marshmallow pillow Max was attempting to use to sleep in an attempt to hear the sound the other two have already heard.
She and both her companions are once again forced to dessert (admit it, you thought of the pun too) their ride as a pair of Cookie Giants, manifestations of Max's desires for his parents to be happy, obliviously eat the cooki the three had been standing on. After briefly commenting on the situation, the group is confronted once again by Mr. Electric, who is this time supported by a legion of Plug Hounds. All three subsequently escape aboard a banana-split themed boat born of Max's imagination, journeying over the sea of confusion to the Ice Princess' castle. Lava Girl halts at the beginning of the narrow bridge of ice before the castle's entrance, fearfully asserting that her firey nature will destroy the bridge. Shark boy proposes sleep-walking, which goes mostly successfully until Mr. Electric and his Plug Hounds once again catch up to the trio. Lava Girl is awaken by a panicked Shark Boy, and her frustration causes the bridge to collapse. All three are easily subdued and captured by Mr. Electric, who brings them before Linus, who masquerades as the deposer-turned-ruler Minus. After a brief and surprisingly genre-savvy monologue, he imprisons them below in a metal cage. Lava Girl claims her powers are weakening and fails to melt the bars. Shark Boy eventually succeeds where she failed, driven into a rage by "La Las". All three make a hasty escape, nabbing Max's Dream Journal and setting out for the Ice Castle.
Though they make good time, Lava Girl is frozen by a false Crystal Heart.
She eventually thaws, in time to remark that the genuine Crystal Heart, now in Max's possession, will not work for anyone but the Princess herself. Mr. Electric once again appears, baiting Shark Boy into a swarm of Electric eels, who knock him unconcious. Noting that Shark Boy will suffocate, as his gills require forward-motion to function, Lava Girl dives in after, bringing her friend back to the surface at the cost of her own health and power. Shark Boy awakens as Mr. Electric departs, taking Lava Girl to her volcanic birthplace and immersing her in the magma there, She awakens more powerful than ever, with the epiphany that she is Light, not destructive flame, and proceeds to cleanse the Darkness from a large portion of Drool as Max confronts Minus. Later, on Earth, she saves Max's mother from the tornados born of Mr. Electric's presence.
In the epilogue, she is seen ruling over Earth's submarine volcanos alongside Shark Boy and assisting him in his search for his father. The two hold hands along a picturesque beach as the film concludes.
Some time later, a bored Lava Girl has further adventures with Max, which are chronicled in a pair of companion novels.
Lava manipulation: Being the queen of volcanoes, Lava Girl possess the ability to control and generate most forms of lava, making her very dangerous in combat.
Light : Lava Girl discovers she is the key to defeating the darkness and lights up the sky with the power and brightness of the sun, potentially making her the most powerful being on planet drool.
Water: When submersed in large quantities of water, Lava Girl will go into an almost death-like state unless she is submerged in Lava.