Rheanimum is a substance is in the Generation One continuity family.

Rheanimum is a rare gas that is mined on Tykos, a moon of E'Brutoc. It makes metals super-dense. Handy stuff if you're made of metal.


Marvel Comics continuity

Megatron led his newest warriors (the Laser Rods and Rotor Force) to capture the rheanimum stores on Tykos. New Dawn

When the Swarm attacked the combined Autobot-Decepticon forces on Earth, the rheanimum was distributed among the allied Transformers, in hopes that its properties would render them invulnerable to the Swarm. It worked. However, in Jhiaxus' flagship in Earth orbit, Optimus Prime refused the rheanimum offered to him by Starscream; in order for his desperate gamble to work, he needed to be consumed by the Swarm! A Rage in Heaven!

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