Originally Posted by Krumm
While that is right in regards to MOS, I didn't see it as a "new" kryptonite but more an introduction to the real thing if it's introduced in later films.
It was and it wasn't new. They re-imagined what it means. Kryptonite is not just some green rock nor is it something that is easy to produce either (it can also be deadly to humans as well). We all know that if Superman was on Krypton, he would become mortal, but the fact that his body would attempt to reject the environment as he acclimated is something never seen before in the comics or in any other media (so you could say that is new). I don't think they have to use a green rock in later films since in this film they established that you can weaken him or turn him mortal by exposing him to that environment (which can be a much harder thing to do than one might think -- I'm pretty sure that someone like Lex Luthor could figure it out, though).