Jane Doe

An unidentified woman, known only as "Jane Doe" and dubbed "Bizarro" by Cat Grant, is a brain trauma patient that was transformed by Lord Technologies into a clone, of sorts, of Supergirl.

Biography
Originally an unknown comatose victim, the woman that became Bizarro was kept in a locked room at Lord Technologies, where she was kept on a drip (containing black liquid) under Maxwell Lord's orders.

Eventually. J'onn J'onzz later sneaks into her room to photograph her on behalf of Alex and Kara Danvers and later deduced her as being injected with hydrochloric acid, showing she was being preserved and altered somehow by Maxwell.

Finally, it is revealed that this girl was transformed into duplicate of Supergirl, with disappearing black eyes, all the while conditioned to hate Supergirl, and if all went according to plan kill her.

However, her form became unstable after being exposed to green Kryptonite, and her initial Kryptonian powers of heat vision and freezing breath were flipped to freeze vision and fire breath, as well as gaining a degenerated physical and mental constitution. After kidnapping James Olsen due to sharing the affections of her progenitor, Kara stops her using a blue version of Kryptonite. In the compound, Kara tells her she and the DEO would take care of her, and the woman known only as Jane Doe was put in a preserved state, so she wouldn't cause harm to others or herself.

Powers

 * Reverse Kryptonian physiology: While retaining most of a Kryptonian's natural abilities, the attributes that give her the abilities of Super Breath and Heat Vision are somewhat reversed in the sense that she creates the opposite of the two each time she accesses her powers. Instead of shooting beams of heat, she shoots beams of pure cold, instead of freezing breath, she breathes fire. She also appeared to have a degenerated form, whether the damage was only surface level is unknown. It can be noted that this transformation could've solely been because of her reactions to the effects of Green Kryptonite, and might have kept her original abilities and intelligence if she was never exposed.
 * Super strength: Bizarro is much stronger than a normal human and equal to Supergirl, allowing her to fight on par with the latter in combat.
 * Super speed: Bizarro is able to move alarmingly faster than a normal human.
 * Flight: Bizarro is able to fly and levitate like a Kryptonian.
 * Invulnerability: Bizarro is resistant to nearly any form of physical attacks or damage that would otherwise be lethal or fatal to a normal human.
 * Fire breath: Bizarro is able to exhale fiery blasts from her mouth.
 * Freeze vision: Bizarro is able to shoot purple bluish freezing beams from her eyes.
 * Kryptonite immunity: While causing her pain, Green Kryptonite doesn't exactly affect her as it would a normal Kryptonian. According to J'onn, green kryptonite has properties which strengthen her.

Weaknesses

 * Blue Kryptonite: A blue version of Kryptonite, a compound with the exact opposite molecular structure, is able to harm and subdue her. However, it also caused her to become calm, rational and understanding, resulting in her accepting being put into a coma to not endanger others and herself along with asking for forgiveness from Supergirl for her actions.
 * Diminished intellect: Having been brain dead for several months, genetically transformed into a clone of Supergirl, and then mutated by Green Kryptonite, Jane Doe has a very warped view on the world in her Bizarro form. Supergirl said that she "spoke like Cookie Monster". Ironically, it's only when struck by her weakness of Blue Kryptonite that she was able to think rationally.