Superman gave a piece of kryptonite to Batman to study, even though Batman tried to kill Superman with it during the Tower of Babel story arc.
Kryponite can kill superman, Magic can too. But doomsday actually killed him but he came back. I hate superman though.
Kryptonite is Superman's weakness.
With Kryptonite you can weaken Superman. The planet Krypton was more massive than Earth before it exploded. By bringing Superman into close proximity with a piece of Kryptonite, which is really a piece of his home world, you reduce (or in some depictions remove) his strength and ability to fly, which are the powers derived from his being on Earth. There's still no telling how he flies in outer space.
Blue kryptonite - it improves Superman's health and frees him from red kryptonite's unpredictable side effects. Blue kryptonite only affects Bizarro - he feels weak.
With a Kryptonite condom.
Kryptonite
Kryptonite
green Cristal
Superman has stated that the only man he's afraid of is Batman, and with good reason.
Superman is weak against kryptonite.
Kryptonite robs Superman of his strength.
Blue