Overgirl

"We've been watching you. We've been watching all of you, and how you've squandered the potential of two words. On our Earth, we've developed a meritocracy. We've accomplished greatness."

- Overgirl on the heroes of Earth-1 and Earth-38

Kara Zor-El, also known as Overgirl, is the secondary antagonist of the Arrowverse crossover "Crisis on Earth-X". She is a general from the Nazi-conquered alternate version of the Arrowverse's Earth-1 known as Earth-X. She is the wife of the Earth X version of Oliver Queen, Black Arrow.

She is portrayed by Melissa Benoist, who also portrays her heroic counterpart from Earth-38, and Supergirl's clone Bizarro.

Biography
Kara's pod crash-landed on Earth from the planet Krypton but instead of Midvile, like her counterpart, she lands on a territory ruled by the Third Reich. She would be raised in this world and grow to embrace hate and evil. She would adopt the name Overgirl.

Along with her husband, Oliver Queen (aka Dark Arrow an evil counterpart to Earth-1's Green Arrow) and Reverse-Flash from Earth-1, they would rule modern day Earth-X with an iron fist. However, Overgirl would take in too much ultra-violet rays in her, thus, she's dying. She needs a heart transplant from Earth-38's Supergirl.

During Barry Allen and Iris West's wedding, The Third Reich from Earth-X would invade Earth-1. After a few battles, they capture Supergirl, her sister, Alex Danvers, and many of Earth-1's heroes and bring them to a concentration camp on Earth-X with the exception of Supergirl who they took to Earth-1's STAR labs.

While strapped to an operating table and bathing in artificial Red Sun rays, Overgirl and Supergirl were arguing over ideologies and expressed how one felt the other was wasting their potential. While Supergirl told her she should have spent her time helping humans and setting a good example, Overgirl countered saying she should have ruled her planet and bring order to it.

Supergirl was initially saved by Iris West and Felicity Smoak, but was captured again. Thawne then tried to carve Supergirl's heart from her body so she can place it in Overgirl's. But was thwarted by Ray Palmer who along with Felicity, and Earth-1's Oliver Queen, rescuing Supergirl, however, this time Oliver threatens Overgirl to either let them go, or he would cut her throat, though Oliver gave his Earth-1 counterpart a chance to save Overgirl with the help of STAR labs. Thawne rescues both Overgirl and Black Arrow.

During her final conflict with Supergirl, the solar radiation within Overgirl's body was overloading and was building up to detonation, essencially, turning her into a bomb getting ready to explode. In a large atomic explosion in Orbit, after Supergirl flew her up high enough so that she wouldn't harm anyone else, Overgirl dies. Black Arrow would try to kill Oliver Queen to avenge her and make sure she didn't die for nothing, Oliver shot him in the heart with an arrow, killing him and making sure Overgirl's death was in vain.

Victims
Indirectly
 * Alex Danvers (Earth-X)
 * Darrel Dane / Dollman (Earth-X)
 * Unnamed minister
 * Numerous unnamed people
 * Tommy Merlyn / Prometheus (Earth-X)
 * Martin Stein / Firestorm
 * Herself

Trivia

 * Her death is very similar to Legends of Tomorrow villain's death, Valentina Vostok in the first season. Being that both died in an explosion due to overload of radiation.