Noxia

Noxia was a large 'Super-Earth' planet which rained molten iron and diamonds. Noxia was roughly five times as massive as Earth, with 33 times as much surface pressure, due to the intensely thick atmosphere.

Noxia was home to ultra-resistant beings, Noxians, who were hyperintelligent but lacked basic verbal communication skills. These beings constructed large underground cities and were renowned throughout the Omniverse for their prowess in medical sciences.