This article contains information that is considered canon in the "Steven Universe" universe.
Even though we've already won the fight for Earth, we're still trying to keep it safe! There are battle-damaged Gems that are still around, and they're not like us. Something's really wrong with them. They're like horrible monsters. We have to poof their bodies away, and then keep their Gems inside of bubbles, so they can't form again and hurt anybody. Maybe someday I'll be able to heal what's wrong with them, but I'm not sure how. Mom couldn't fix them either. For now, we're keeping them safe inside the Temple.
|—Steven, "Guide to the Crystal Gems"|
Corrupted Gems, also known as Gem Monsters are Gems who have become corrupted assuming monstrous and nigh-incoherent forms. One of the main missions of the Crystal Gems other their protection of humanity is to defeat, contain and hopefully cure them.
Corrupted Gems used to be normal Gems prior to the events that unfolded at the end of the Rebellion. As a last ditch effort in the war for Earth, the Great Diamond Authority sent out a Corrupting Light which corrupted gems from both Homeworld and the Rebellion that had been left on Earth, most likely a means of ensuring the rebellion couldn't directly threaten Homeworld. In "Monster Reunion", the Centipeetle Mother described it as a "song" and remembering it seemed to be what triggered her to revert back into her corrupted form.
It's sort of like if MC Bear-Bear didn't tear the fabric of his arm, but the fabric of his mind.
|—Garnet, "Monster Reunion"|
Corruption also changes the physical appearance of a Gem's gemstone. As Centipeetle's gemstone had a curvy contour line that surrounded the circumference of the gem, and upon partial healing by Steven, the curvy contour line straightened.
Most corrupted Gems are hostile and dangerous. However, much like regular Gems, when their bodies are severely damaged, they explode into smoke, or "poof", leaving their gemstone behind. The gemstone can then be safely contained in a Gem bubble, preventing it from regenerating. Some corrupted Gems are imprisoned in objects (such as the Pyramid Temple's gemstone), which also prevents them from regenerating.
Corruption also seems to strip gems of some of their basic powers. They are unable to summon their weapons or use warp pads and other Gem structures, such as a door to a spaceship.
Garnet simply describes corruption as a tear in the mind of a Gem, rather than physical damage on their gemstone and as such is harder to heal than a cracked Gem. There is one known way to heal corrupted gems and reverse the effects.
Steven's healing spit only partially and temporarily healed the Centipeetle Mother, but she reverted to her corrupted form shortly after. Garnet acknowledges this as a major step in trying to heal the Corrupted Gems even though Steven's attempt had failed, saying that it was the best that they've seen it work. She indicated that Rose Quartz was unable to heal the Corrupted Gems to the same extent her son, Steven, had done.
Known Corrupted Gems
- Centipeetle Mother
- Pyramid Temple Gem
- Worm Monster
- Desert Glass
- Big Bird
- Heaven Beetle
- Earth Beetle
- Gem Cave Creature
- Watermelon Tourmaline
- Ice Monster
- Invisible Gem Monster
- Lighthouse Gem Monster
- Water Bear
- The Slinker
- Crab Gem Monster
- Unknown Giant Gem Monster
- Minor Corrupted Gems
- Green Great North Monster
- Orange Great North Monster
Comic book series:
- Obelisk (comics)
- Rainbow Cloud Monster
- Slug Monster
- Plant Monster
- Invisible Manta Ray
- Clock Tower
- Unknown Giant Bird
- The Perils of Pweepwee
Steven and the Crystal Gems
- Glass Ghost
- When regenerating, the Centipeetle Mother briefly assumed a humanoid shape - presumably reflective of her original form.
- It's unknown how many of the corrupted Gems are former Homeworld Gems and how many are former Crystal Gems.
- Some corrupted Gems, such as the Worm Monster and the Centipeetle Mother, are shown to have an urge to eat food. The reasons for this are unknown, but it is possible that they do not gain sustenance from their gemstones like most other Gems do.
- Unreleased corrupted Gems can be seen on Guy Davis' Tumblr, such as the Stinger, the Fist Chest, and the Shell Back.
- Garnet's description of the difference between cracked and corrupted gems in "Monster Reunion" is spot on. Where gem cracking can be represented by significant physical damage, gem corruption could be representative of mental damage. The etymology of "schizophrenia" is "the splitting (or tearing or fracturing) of the mind", a word that for years was used to broadly describe just about any mental illness until the 1970s when significant changes to how mental disorders are diagnosed. Schizophrenia does not imply that a person has multiple personalities. That diagnosis belongs to Multiple Personality Disorder, which is a completely different diagnosis and is often not related to schizophrenia. The most common mental disorders are anxiety disorders (including PTSD) and depression. How the series will handle the issue of gem corrpution is still to be determined but it is quite clear that it will be the topic of future episodes.