Stepsister from Planet Weird is a Disney Channel Original Movie, first aired in 2000.
Megan Larson is an ordinary teenage girl. Her workaholic father Fred and windsurfing mother Kathy are divorced, and Megan longs for them to get back together, as much as she wants her little brother Trevor to be less annoying. But the thing she wants the most is for a popular guy named Cutter to be her boyfriend.
But things start to get a little weird when her mother meets Cosmo Cola, a nice but weird guy. He has a pretty and intelligent daughter named Ariel who is even weirder than her dad. Ariel hides under her father's car when the wind blows, talks in a sophisticated manner, wears many layers to "protect her essence", cannot ride a bicycle despite using training wheels, and often complains that she hates the town where she resides and wants to return to her hometown in Canada to be with her boyfriend, Fanul. Worst of all for Megan, the kids at school think that the quirky way Ariel behaves is "cool and revolutionary". Her teachers believe her mannerisms are poetic, and she even gets to sit at the popular table on her first day which attracts Cutter's attention.
What Megan does not realize is that Ariel and her father are actually alien refugees. Cosmo was a freedom fighter back on their home planet of Zircolon fighting against the oppressive government. They had to escape to Earth, leaving behind their home, Ariel's mother (who was killed on the way there), and Ariel's boyfriend Fanul, the son of the emperor. Ariel and Megan can't stand one another, which only gets worse when Megan's mother becomes engaged to Ariel's father. As Ariel and Megan realize that they both want to separate their parents, they agree on a temporary alliance to achieve their common goal. However, none of their plans work well.
When Megan begins to suspect something especially unusual is occurring, she discovers that both Ariel and Cosmo are aliens. Hilarity Ensues.
This movie contains the following tropes:
- Adaptation Distillation: Ariel has many more powers in the original book than in the movie.
- In the book, Kathy is a regular board surfer. This was changed to windsurfing in the movie, as it was easier for the actress to learn and is much more photogenic on film.
- Alien Among Us: Cosmo and Ariel are forced to flee their home planet Zircalon and take refuge on Earth.
- Aliens Speaking English: Every alien that comes to Earth immediately can speak perfectly fluent English.
- Amazingly Embarrassing Parents: It seems this can happen on any planet.
- Amusing Alien: While Cosmo acclimates to human life rather well, he is still out of touch with what is considered good manners for human social interactions.
- Annoying Younger Sibling: It's played straight, and subverted at the same time with Megan's brother Trevor.
- Betty and Veronica: Mentioned by name referring to Megan and Ariel. Ironically, not only does Megan's crush fall for Ariel, but Ariel's boyfriend from Zircolon, Fanul, ends up falling for Megan.
- Blow You Away: At the climax, Trevor uses a leaf blower to push the Emperor (in his bubble form) into a tree, popping him.
- Bizarre Alien Biology: Ariel and Cosmo's true forms are of gaseous bubbles that float carelessly and they subsist on carbon dioxide. On the other side, Ariel thinks humans have weird forms.Ariel: (inwardly narrating) Every time I look at this horrid vehicle - the rubbery flesh, the flat face, the ghastly yellow hair that grows out of this hideous skull - I can only think I am grotesque.
- The Caligula: The Emperor of Zircolon does not like it when people disrespect his authority.
- Crazy Cultural Comparison: Much of the humor comes from Ariel comparing how weird she thinks human culture is compared to back home.
- Crouching Moron, Hidden Badass: Cosmo might be a childish weirdo on Earth, but he was a famous freedom fighter back on Zircolon, wanted by the emperor himself.
- Didn't Think This Through: Megan and Ariel's plan to break up their parents because they don't like each other. It didn't occur to them that they'd find they actually had a lot in common.
- Everytown, America: Though this one takes place in Hawaii.
- Fantastic Comedy: A comedic movie where an alien and a human fall in love, much to the consternation of their respective kids.
- Fire-Forged Friends: After mutually disliking one another for the whole movie, Megan and Ariel become this once Ariel reveals the truth about herself to Megan and they defeat the Zircolonian Emperor together.
- Foreign Queasine: Ariel's idea of a dinner involves blending all the food into an unrecognizable paste. When asked, she points out that all if it eventually ends up in the intestinal tract, so why bother with separating it?
- Full-Name Basis: Ariel refers to Megan by her full name at first, but as they grow more friendly with each other, she drops this habit.
- Humans Are Bastards: Averted. Not only do humans help Cosmo and Ariel, Megan and the others manage to help topple an evil alien empire.
- Human Aliens: Cosmo, Ariel, Fanul, and the emperor are actually sentient gas bubbles, but take human form on Earth.
- Human Outside, Alien Inside: Again, Cola and Ariel. Their real forms are gaseous bubbles, but living on Earth forces them to adapt flesh bodies.
- Informed Attribute: Cosmo is called a "great" freedom fighter, but he is never seen being great at fighting (he was only portrayed as someone running from Emperor S'vad and telling Emperor S'Vad to take him instead, with no mention of him actually fighting for freedom).
- Interspecies Romance: Between Megan's mother and Ariel's father. And later, this happens between Megan and Fanul, and Ariel and Cutter.
- Involuntary Shapeshifting: Ariel has this habit of turning herself into her true bubble form in soapy water.
- Literal-Minded: Cosmo and Ariel have some trouble understanding idioms, sarcastic remarks and indirect language. For example, when Kathy tries to have a serious conversation with Cosmo about what he finds attractive about her, his answer boils down to "fun and cute." Kathy asks what he thinks about her mind. Confused, he replies that he has never seen it (after all, it's not a physical object that can be seen). She is not amused at the answer. Still, their oddities are generally written off as being "Canadian" (from the Yukon).
- Mad Dictator's Handsome Son: Fanul is a much nicer and affable person compared to his despotic father, and after his father is defeated, he promises to grant the Zircolonians a freer society.
- Meaningful Rename: In-universe. Cosmo likely chose Cola as their human surname because, as gaseous bubbles are their true forms, soda also contains carbon dioxide bubbles and serves as their "comfort food".
- Oh, Crap!: When Megan first discovers the truth about Ariel, they both scream.
- Relationship Sabotage: In this case, the people doing the sabotaging are the kids who don't want their respective parents getting together.
- Romantic False Lead: To break up their families, Ariel tries to arrange a dinner with her father and a fortune teller named Serena, and Megan tries to get her mother back together with her father. It doesn't end well, ironically, as Serena ends up with Megan's father instead.
- Shout-Out: When Trevor fakes sick, he calls out "Elizabeth, I'm coming to join ya!". Cosmo even shouts out "Fred Sanford! Excellent!" in response, showing his recognition of Earth pop culture.
- Testosterone Poisoning: As part of the sabotage, Ariel suggests to her father that Megan's mother wants a "stronger man", and Cosmo starts trying to act like one, including talking like a cowboy and ordering a steak in a pizza restaurant.
- Trademark Favorite Food: Root beer. Upon landing on Earth, Ariel won't eat anything else. She only likes soda because it contains carbon dioxide.
- The Ugly Guy's Hot Daughter: Ariel Cola, though in all fairness, Cosmo's not that ugly.
- The World Is Just Awesome: Mr. Cola thinks all of Earth is pretty cool.
- Worthless Yellow Rocks: Ariel complains that packing a bunch of worthless crystals from Zircolon wasn't going to help them on Earth, but Cosmo makes a fortune selling them on his online business (Cosmo's Diamonds) and subsequently uses the cash to support the family and buy a collection of odd things to gift to Megan's mother.