Eternium is the most powerful substance on the planet Eternia. Just a little piece can act as a source of energy for the city of Eternos for a long time. It's almost impossible to find. If Trap Jaw eats Eternium, he becomes as strong as He-Man, if not stronger, but the substance is poisonous for other beings. There's a similar-looking substance named Deterium, but it's useless for anything.