|List of all weapons & other items|
Thundrainium is a highly unstable and dangerous substance found on Thundera as well as Third Earth. It emits radiation which severely weakens ThunderCats while not being particularly harmful to any other beings. Due to its devastating effects on the ThunderCats, their enemies have utilized Thundrainium many times in order to try and defeat the Cats. Grune forged his Battle Club from Thundrainium while Vultureman built a Thundrainium Cannon to battle the ThunderCats.
On Third Earth, Thundrainium is commonly known as "Fire Rocks" and is present in abundance on Fire Rock Mountain. Due to its unstable nature, it has been forbidden to mine for it on the planet for at least a hundred mega years.