Libby is a 12-year old girl with brown eyes, darkish pink eyelids, and black hair.
In the movie, shorts, season one, and temporarily in Beach Party Mummy, Libby wore a turquoise dress with blue, green, and orange patterned rectangles on it, turquoise green knee high socks, and black Mary-Jane shoes with a gold buckle. She also had a streak of her hair covering her right eye along with her hair in a high bun held by a hair tie that matches the pattern on her dress and her eyelids were red.
In "Beach Party Mummy", Libby is given Egyptian dreads as part of Jimmy's plan to make Libby look like her ancestor, Queen Hasabataslapya and put the mummies to sleep for 10 trillion more years. Libby likes the hairstyle so much that she decides to keep it. In the next episode, Libby gains new clothes; a striped pink fading shirt, blue jeans, brown shoes, and a pink choker collar.
She was seen in her underwear in "Patrick the Snowman." It is two pieces and consists of a similar color scheme to her dress.
In the N Men, as Invisible Sister, she wears a blue bodysuit with matching boots and finger-less gloves with a silver lining and a silver belt.
In Crouching Jimmy, Hidden Sheen, she wears a sparkly red shirt, with a purple stripe on the bottom, as well as black flared jeans and white shoes. She also has on blue eye shadow, red lipstick, and a beauty mark on her left cheek.
Not much is known about Libby's family, but she is known to have a father and mother. In "Beach Party Mummy," she discovers that she is related to Queen Hasabataslapya, and changes her hairstyle to the one her ancestor wore in her portrait. She is a vegetarian.
In the shorts, movie and early episodes, Libby was more of a flat character, but as the series progressed, she became more of her own character and evolved into the group's voice of reason.
Libby's main interest is hip-hop, R&B and funk music. When she experiences music withdrawal, she faints and goes crazy. She also loves electronic gadgets and being stylish. In the first and second season, she doesn't appear in the title logo. When she becomes more involved in the show, however, she is added to the logo in the third season. Unlike Jimmy's other best friends, Libby is shown to be very book smart, but is not a super genius like Jimmy and Cindy. Libby also is very honest and cannot lie at all, which often gives complications to Jimmy's plans or keeping secrets. Although she does lie in Jimmy for President and Attack of the Twonkies, which the gang is understandably shocked by.
Her favorite band is Graystar, whom she sometimes asks to play at Retroville. She is also revealed to have piano playing skills.
Along with Cindy, Libby won a first place trophy for Riverstomp dancing at the school contest in "Battle of the Band;" Jimmy, Carl, and Sheen almost beat the girls with their electronic rock music guitars and drums, but at the last minute, Carl and Sheen destroyed their own instruments in a jealous quarrel, and the boys ended up with was an eighth place trophy after Carl did his giant snot bubble trick.
Libby has full knowledge about Jimmy and Cindy's relationship with each other, as Cindy does not want to express her feelings to Libby about it and stammers each time Libby mentions it. Although, Libby sometimes joins Cindy in teasing Jimmy and can be apathetic to their fake fighting. Libby returns Sheen's interest in herself, but not when Sheen is not annoying her with his overbearing mentions of Ultra Lord and occasional flirting, and sometimes Libby denies that she likes Sheen. Sometimes though, it is hinted that Libby might be a fan of Ultra Lord as well.
In "The Tomorrow Boys", Libby had become the evil dictator of Retroville after Carl accidentally got the Megalomanium to her birthday party out of confusion by the perfume and the Megalomania. When she opened the present, she became mad with power, thus making her the evil dictator of Retroville. When Jimmy, Carl, Sheen and Goddard saved the future, she got mad at them for destroying her gifts and ruining her party. When Sheen explains everything and apologizes, she forgives him and realizes how much Sheen cares about her.
In "Crouching Jimmy, Hidden Sheen", Yoo-Yee kidnaps her, so he can take Sheen's place as the Chosen One in Shangri-Llama. Sheen goes to rescue her and defeats him after Libby admits to being his girlfriend. Libby also realizes that Sheen cares about her more than Ultra Lord. It is also revealed that she cares about him more than music.
In "The N-Men", Libby gains the super power of invisibility, based on how she was putting on vanishing cream when she and the group were exposed to the Van Patten Radiation Belt. Libby calls herself "Invisible Sister". She learned in the military station that she also had the ability to generate a force field and create a pad to float herself in midair.
In The League of Villains, Jimmy, Carl, Sheen, Cindy and Libby's superpowers are mixed up, thanks to Carl's incompetence. Libby is the one who had ended up with Carl's superpower; Burp Boy. This made her gain the ability to make gigantic burps enough to make anyone go flying.
Libby is smart enough to know that even some of Cindy's own absurd antics can go a little too far, earning a snide remark or a slight hint of disappointment from Libby (making her a bit of a foil), especially since she is well-aware of Cindy and Jimmy's feelings towards each other. Cindy is also aware that Libby likes Sheen.
In the shorts, the movie and season one, Libby was more of a sidekick to Cindy and didnt have much of a role in the franchise, but since then, she's become more of her own person and the gang's voice of reason.
Brittany often appears as a third member of Cindy and Libby's circle of friends, usually for singing, dancing or just for hanging out. One time, Brittany bribed Libby into being her science partner with a shiny new CD. While Libby and Brittany don't hang out as much as she and Cindy do, they're very good friends and get along well, although Cindy and Libby sometimes pick on Brittany.
Libby and Sheen weren't quite close friends at the beginning, however Libby does encourage and compliment Sheen when he comes up with a good idea. For instance, in Beach Party Mummy, when Sheen distracted Principal Willoughby by telling him that new school tanning salon had been opened, Libby smiled and responded to Sheen's idea with "Great thinking Sheen!" The two were even seen dancing alongside each other in the same episode. Libby also always sticks up for Sheen whenever somebody yells at him or mocks him. A good example is at a scene in the Yolkian dungeons in the movie.
Their friendship eventually blossomed into a relationship during the episode of Love Potion 976/J, where Sheen was accidentally exposed to Jimmy's love potion and suddenly fell in love with Libby. After the effects were reversed, Sheen still liked her and Libby showed him that she did like him back. From then on, Sheen has shown interest in her and is always looking after her, but it is hinted in previous episodes that he's always liked her. While Libby doesn't always approve of the nicknames which Sheen makes up, she returns his feelings and thinks he's cute and funny. In Crouching Jimmy, Hidden Sheen, she finally becomes Sheen's girlfriend after defeating Yoo Yee. We also learn that Sheen actually cares about her more than Ultra Lord and that she cares about him more than music. Sometimes though, Libby denies liking Sheen out of embarassment.
In Planet Sheen, Sheen gets a new love interest and his and Libby's relationship is abandoned because of it. It is unknown if they were still together at that point, or if Planet Sheen is even canon.
Libby acts somewhat sisterly to Jimmy and is always trying to get him to come out of his shell. Jimmy likes Libby because she's calm, mellow and sensible.
In Crouching Jimmy, Hidden Sheen, Yoo-Yee thought Libby was Sheen's girlfriend, so he tried to kidnap her to urge Sheen coming to Shangri-Llama and fight him. He tried to be nice to Libby and even gave his sister's room to Libby, but she didn't like it because her CD collection was totally beat and hated the wallpaper. However, Libby did like Yoo-Yee's sister's jewelry. She was also angry at Yoo Yee for senselessely beating up Sheen, which gave Sheen the proper motivation and made him defeat Yoo Yee.
- "Keep yellin' if you wanna mirage slap in yo FACE!!" - Stranded
- "Sheen, none of those things even do any of those things..." - Stranded
- "You can't stop da' funk...ya mamma can't stop da' funk--AH AH--yo brotha' can't stop da' funk..." - Stranded
- "Give it up for JIMMY!!! We believe in you, Jimmy!" - The Eggpire Strikes Back
- "Open your EYES, girlfriend! I'm right in FRONT o' you!!" - The N-Men
- "We hafta WHAT?!!" - Substitute Creature
- "Why don't we just go after the dog??" - Jimmy Timmy Power Hour
- "But my mama told me not to burp in public!!!" - The League of Villains
- "Ladies, there's this spanking new band called Graystar and all I'm asking you is to stop walking away while I'm talking to you!!!" - Attack of the Twonkies
- "Yeah, or we could play 'Spin-Sheen-and-hit-him-with-a-bottle'." - Party at Neutron's
- "Meet me at the Candy Bar, Sheen, (opens door) AFTER YOU CLEAN MY HOUSE!!" - The Tomorrow Boys
- "How come I'm not invisible? (burps explosively) (covers mouth in embarrassment) Excuse me. (explosive belch) Ugh, I'm Belch (explosive burp) Boy?! (loud burp) This is way embarrassing." -The League of Villains
- "Sheen, you better put some hurting on this fool! You hear me?! This is your girlfriend talkin' to you!" -Crouching Jimmy, Hidden Sheen
- "Wait, stop! Carl's not an alien!" ... "What?! Oh, no!" ... "Forgive me, guys?" -Lady Sings the News
- "I was listening to a good song; I have priorities." -The Retroville 9
- "Get your tounge off the floor." -The Great Egg Heist
- "Hey, Cin, put your eyes back in yo' head and let's get to work."-My Big Fat Spy Wedding
- "Here we go, here we go." - Movie
- "100 years of hard labor!" -The Tomorrow Boys
- "Do you have some carrot sticks or maybe some antacid?" -Hypno-Birthday To You
- "Jimmy, don't put up with that! You have to tell a teacher!" -Safety First
- "I'll give you three seconds to get away from my ruby stash!" -A Beautiful Mine
- "That's it! I had it with you and your big freaky head!" -Sheen's Brain
- "AAAHH!!! Our rubies!" -A Beautiful Mine
- "Intergalatic Beat Jam, cool!" -The Eggpire Strikes Back
- "He tried to raid my ruby stash!" -A Beautiful Mine
- "Sheen, let them down!" -Sheen's Brain
- "I'm never getting sick again! That wasp sting really hurt!" -Journey to the Center of Carl
- "Hey, maybe this whole place belongs to me." -Beach Party Mummy
- "Do me a favor, the next time I suggest we humiliate somebody, DON'T LISTEN!" -Holly Jolly Jimmy
- "Sheen, you're usually weird, but tonight, you've got a little extra going on." -Nightmare in Retroville
- "Cindy, are you really going to let those two guys fight over you?" -Jimmy Timmy Power Hour 2: When Nerds Collide!
- "Hey Sheen, you said we were going to get something to eat, how about Jimmy?" -Nightmare in Retroville
- "Sorry I'm late, my paddle broke so I had to row my desk to school with this plastic leg." -I Dream of Jimmy
- Libby is one of two females in the franchise to burp, the other one is Judy.
- She is eleven years old (twelve starting with "The Tomorrow Boys").
- Libby is the second protagonist in the franchise to become evil. The first one was Sheen.
- It is unknown why Sheen doesn't mention her or bring her up in Planet Sheen, or if they were even still dating at that point.
- Libby's bad future counterpart looks more like her original design than her current one.
- While Libby loves music, she thought Yoo-Yee's sister's CD collection was totally beat.
- Libby has a little brother (who's name has not been mentioned and looks was unseen in the series) seen in the beginning of "Make Room for Daddy-O" as the legs in the saw the lady in half trick.
- Sometimes it is hinted that Libby may like Ultra Lord too.
- She is a vegetarian.
- Her birthday is December 12, the same day as Frank Sinatra's, so she's a Sagittarius.
- Even though Libby cannot lie, she does uncharacteristically lie in A Beautiful Mine, Attack of the Twonkies and Jimmy for President, which her friends get understandably shocked by.
- In The Incredible Shrinking Town, it is revealed she doesn't care about Jimmy endangering the town anymore.
- Originally, Libby and Nick were going to be cousins.
- Libby's original design bears a huge resemblance to Keesha Franklin from the Magic School Bus.
Villains: King Goobot V | Professor Calamitous | Eustace Strych | Beautiful Gorgeous | Meldar Prime | Evil Jimmy | The Junkman | Zix, Travoltron and Tee | Baby Eddie | Gortox the Irritable | Dr. Sydney Moist