Skylar Storm

Skylar Storm is a main character in the series, Mighty Med. She was a superhero from the planet Caldera whom Kaz and Oliver admire, the latter of whom has a crush on her. Once a great superhero, she lost her powers when her arch enemy the Annihilator stole them, but turned evil upon regaining them. With Skylar serving the Annihilator, she has become one of the most dangerous supervillains to be reckoned with.

Skylar serves as the secondary antagonist of Season 2 in Mighty Med.

Origins & Life as a Hero
Skylar Storm was once a superhero born on the volcanic planet Caldera, whose people are genetically engineered with superpowers. Skylar has faced off with some of the most fearsome villains in the world. Beware to anyone who treats her as "just another pretty face!" One day, her arch enemy, the Annihilator, confronted her and stole her powers, reducing her to a normo who relied solely on her agility and reflexes in combat. Kaz and Oliver decided that one day, they would find a way to restore her powers.

Turn to Evil
One year later, Kaz and Oliver found the Annihilator's lair and stole back Skylar's stolen powers, though the Annihilator eventually followed them to Mighty Med. After Skylar's powers were restored, she ended up becoming controlled by the Annihilator's evil. It was eventually revealed that the Annihilator used a serum to tamper with Skylar's powers so that he could control them once she regained them. After Skylar found a way to reverse time, everyone involved would forget that she turned evil, and would continue serving the Annihilator as a mole. The Annihilator later had Skylar use his serum to turn other superheroes into his evil servants. Later on, Kaz and Oliver found out she was evil, but kept it secret so that Skylar wouldn't suspect them. Kaz and Oliver resolve that they must find a way to defeat Skylar and the Annihilator.

Loose Ends
The Annihilator decided that Kaz and Oliver were to dangerous as they kept interfering in their plans, and ordered Skylar to kill Oliver first. Skylar asked Oliver to the dance, planning to kiss him and steal his life (due to a power the Annihilator gave her) but during the dance, her feelings for Oliver started to conflict her. She went back to the Annihilator to try and convince him that Oliver didn't need to die. However the Annihilator was furious she had disobeyed him and told her do it or he would kill her himself, and then her. Back at the dance Skylar tried again, and reluctantly tried to kiss him. However they were interrupted by Alan and Skylar lost her nerve. Returning to the Annihilator she lied that she had suceeded.

Final Battle & Defeat
When Kaz and Oliver visited Caldera, The Annihilator and Skylar ambushed the boys at Hapax the Elder's hideout. Kaz and Oliver make their final stand against Skylar, who has decided to betray the Annihilator and rule the universe, but not without offering Kaz and Oliver to join her. Oliver pretends to give in, but in truth, got close enough to give her coal, her one true weakness. Now weakened with the help of Hapax the Elder, Skylar was defeated. Hapax sucked out Skylar's corrupted powers, turning her good again but leaving her powerless.

Trivia

 * Skylar is very similar to Darth Vader in that both started out as heroes, but then turned evil and subservient to the main antagonists.  Both have a connection with the main protagonist, and that connection gave them conscience to prevent them from killing them.