|This article belongs to the Classic Continuity|
Element X is a rare mineral substance.
Element X typically looks like a small pink rock with slight cracks and usually is kept in a protective tube of hard glass with metal caps.
A sample of Element X was stored in a secure facility until it was stolen by Vulkanus and Sixsix while being transported. When combined with Bicenthium Alloy (the alien name for iron ore), it creates an explosive powerful enough to obliterate an entire solar system. Element X is useless by itself, however.
Element X and Bicenthium alloy can only be bound together with an enormous amount of heat. 
Element X requires careful handling when dealing with its explosive counterpart. Contact with the unbounded iron ore can create a small explosion, which is enough to severely injure anyone caught in the explosion.
Element X can be used to power certain ships, such as Sheelane's, and was found on her home planet, Thalassia, prior to its destruction.
Element X, by its very nature and rarity, attracts alien criminals, such as the likes of Vulkanus.
- The Galactic Enforcers (first appearance)
Ben 10: Omniverse
- The Ballad of Mr. Baumann (first re-appearance)