Superman and Kryptonite

Surely everybody knows that Kryptonite is about the only thing that could strip Superman of his powers and, eventually, kill him. Lex Luthor, Metallo and even Batman have used this rare mineral in order to temporarily disable the Man of Steel.

The drawback is that any Kryptonian could become immune to kryptonite if he is exposed repeatedly. So, if the superhero isn't killed from the first time, then most definitely a second time wouldn't follow.