Stepsister From Planet Weird

Stepsister from Planet Weird is a Disney Channel Original Movie. 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 training wheels and a football helmet, and mostly complains that she hates the town where she resides and wants to return to her hometown in Yukon to be with her boyfriend, Fanul. Worst of all for Megan Larson, the kids at school think that the way Ariel behaves is 'cool and revolutionary'. Her teachers believe her mannerisms are poetic, and she even gets to sit in the popular table on her first day which attracts Cutter's attention.

What Megan does not realize is that Ariel and her father are aliens. Because Ariel's father was a freedom fighter on their home planet, they had to escape to Earth, leaving behind their home, Ariel's mother, and Ariel's boyfriend Fanul, the son of the emperor (surprise). On her home planet, every citizen is a gaseous bubble that floats carelessly, so Ariel is very uncomfortable with the solid objects of Earth. She hates everything on Earth: her name, the wind that blows, the solid objects and people, "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." Ariel and Megan become enemies although 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. When she does find out... Hilarity Ensues.

The movie contains the following tropes

 * Alien Among Us
 * Amazingly Embarrassing Parents: It seems this can happen on any planet.
 * Amusing Alien
 * Annoying Younger Sibling: It's played straight, and subverted at the same time.
 * Bratty Teenage Daughter: Arguably Megan at fisrt, but she gets better.
 * Fantastic Comedy
 * Involuntary Shapeshifting: Ariel has this habit of turning herself into a... bubble.
 * Outer Space Astronauts: Brian and Sophie.