Green Kryptonite (UE-44)

"Aren't you curious how I know so much about you, Kal-El? Like me, your home was destroyed. You were sent here as an infant to a world where you'd spend your whole life trying to prove your worth, convince yourself you were one of them, but you're not! You're still that scared, lost child, desperate for the love of people that will never accept you! And the only remnants of your real home, kryptonite, make you sick."

- Luthor to Superman

Kryptonite is a radioactive mineral originated from Krypton.

History
At some point, John Henry Irons was able to acquire Kryptonite after the destruction of Krypton and carved it into a dagger as a weapon against Superman. Following his universe's destruction and relocated to Earth-Prime, the Kryptonite dagger was brought along him and was used against Superman of Earth-Prime.

During the fight between Luthor and Superman, the former lost the dagger after stabbing into Superman's chest and was the last of his supplies.

Functions

 * Kryptonian weakening: When exposed to Kryptonite, the green mineral makes Kryptonians vulnerable and cause dizziness.