A small percentage of fragments floating through space that were formerly Krypton-One passed through a red gaseous cloud in space, transforming not only their color but their nature from green to red Kryptonite. When Superboy first encountered this substance, he found that its effects were temporary and unpredictable, causing varous physical transformations in his physiology more a nuisance than anything else. A similar strand of red Kryptonite formerly part of Krypton-Two was revealed later in the golden age Superman's career, only from a future era. In that instance, used by the criminal Futuremen, this element caused the hero to lose control of his abilities and temporary paralysis in each instance that he encountered it. Which, thankfully, was only once.
Cherry Poptart and The Watcher
11 hours ago