Corrupted Gems are, as it says exactly on the tin, versions of the normal Gems from Steven Universe corrupted into more monstrous versions of themselves, such as Monster Steven. These can take all kinds of shapes and sizes and therefore should not be tagged with gem_(species) since it automatically adds the alien_humanoid tag, unless said Corrupted Gem happens to fit the description of an alien humanoid.

The vast majority of Corrupted Gems were created accidentally by The Order of the Diamonds. Following, the death of Pink Diamond at the hands of Rose Quartz during the Gem Rebellion, the The Diamonds ordered a full-scale evacuation of all Homeworld Gems from Earth. After the evacuation was completed, the remaining Diamonds combined their powers to launch one final direct attack to wipe out the Crystal Gems once and for all. This attack became known as corrupting light. Yellow Diamond, whose power disrupts and alter the physical forms of gems, Blue Diamond whose powers manipulate the emotional state of gems, and White Diamond whose powers affect the thoughts and actions of other gems created a ghastly power that transforms gems into monsters with shattered minds, instinctively attacking most other living things and gems without knowing what they are doing or why.

The only gem that was not corrupted by the Diamonds was Monster Steven.