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, were Gems who had become corrupted assuming monstrous and nigh-incoherent forms. One of the main objectives of the Crystal Gems other than their protection of humanity and Earth was to defeat, contain Corrupted Gems and hopefully cure. In "Change Your Mind" many Corrupted Gems were healed when Steven and The Great Diamond Authority combined their powers at Rose's Fountain.
All those monsters we fight used to be just like us! Right, Pearl?
|—Amethyst and Pearl, "Ocean Gem"|
Corrupted Gems had been normal Gems before the events that unfolded at the end of The Rebellion. As a last-ditch effort in the war for Earth the other Diamonds sent out a flash of bright light which corrupted Gems from both Homeworld and the Rebellion on Earth. In "Monster Reunion" Nephrite described it as a "song" and remembering it seemed to be what triggered her reversion.
As revealed in "Earthlings" second-hand corruption occurs to normal Gems through fusion with corrupted ones as Jasper started corrupting after fusing with Ocean Jasper and forming a semi-corrupted fusion.
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"|
The appearance of Corrupted Gems varies greatly with different Gems although Corrupted Gems of the same type take on similar appearances as shown by the Heaven Beetle and Earth Beetle, Nephrite's crew and various Quartzes. As the bodies of Gems are mental projections, the bodies of corrupted Gems are a reflection of how damaged their minds are. Forms range from slightly humanoid to monstrous and in severe cases not having a physical body at all.
Corruption sometimes also changes the physical appearance of a Gem's gemstone. As Nephrite'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. Jasper's gemstone, however, wasn't changed by her corruption. Time may be a factor in this case - Nephrite had been corrupted for several millennia, as opposed to Jasper, who had just undergone it.
Most Corrupted Gems are hostile and dangerous and behave similarly to wild animals. Many of them will exhibit behaviors such as feeding and predation, despite not requiring sustenance. They are also capable of creating offspring and eggs, such as Nephrite in "Gem Glow". However, much like regular Gems, when their bodies are severely damaged, they explode into smoke or poof leaving their gemstones behind. The gemstones can then be safely contained in Bubbles preventing it from regenerating. Some corrupted Gems are imprisoned in objects (such as the Pyramid Temple's gemstone or Lapis's mirror) which also prevents them from regenerating.
Corruption also seems to strip Gems of some of their basic powers. They are unable to summon objects or use Warp Pads and other Gem technology such as the doors to spaceships.
Garnet described corruption as a tear in the minds of Gems rather than physical damage to their gemstone and as such was harder to heal than cracked gemstones. The power of all four Diamonds was required to entirely reverse its effects; Steven's saliva only partially and temporarily healed Nephrite as she reverted to her corrupted form shortly afterwards. Garnet acknowledged this as a major step in trying to heal the Corrupted Gems even though Steven's attempt had failed saying it was the best they'd seen it work; she indicated that Rose Quartz was unable to heal Corrupted Gems to the same extent.
In "Legs From Here to Homeworld" the combined powers of Steven, Yellow Diamond and Blue Diamond were able to heal Centipeetle back to Nephrite but she immediately reverts to her corrupted form when the three let go of her. Yellow believes that the addition of White Diamond's powers would be able to permanently heal the Corrupted Gems.
In "Change Your Mind" the Corrupted Gems were healed using a combination of the Diamonds and Steven's powers at Rose's Fountain. Most healed Gems carried "scars" of their corruption such as the spikes and teal coloring of Jasper's default form. Aside from this the Gems still held their previous faculties and memories mostly expressing sheer joy and happiness at being liberated entirely.
As of Steven Universe: The Movie the uncorrupted gems seem to have blended into society.
Known Corrupted Gems
- Orange Spodumene
- Heaven Beetle
- Earth Beetle
- Watermelon Tourmaline
- Water Bear
- Nephrite's Crew
- Zebra Jasper (unfused)
- Biggs Jasper
- Invisible Gem Monster
- Snowflake Obsidian
- Cherry Quartz
- Lace Amethyst
- Blue Lace Agate
- Crazy Lace Agate
- Desert Glass
- Big Bird
- Gem Cave Creature
- Lighthouse Gem Monster
- The Slinker
- Tongue Monster
- Flower Monster
- Obelisk (comics)
- Rainbow Cloud Monster
- Slug Monster
- Plant Monster
- Old Book Gem
- Invisible Manta Ray
- Clock Tower
- Unknown Giant Bird
- The Perils of Pweepwee
- Red Bird Gem Monster
- Slime Gem Monster
- Tentacle Monster
- Red Eel Monster
- Monster Lizard Gem
- Mole Gem Monster
- Vine Monsters
- Frozen Fragment
- Scorching Shard
- Mollusks (presumed uncorrupted, status unknown)
Steven Universe and the Crystal Gems
- Glass Ghost (presumed uncorrupted, status unknown)
- Ant Gem Monster (presumed uncorrupted, status unknown)
- Light Green Corrupted Gem
- Mauve Moth Monster
- Lonely Pearl (presumed uncorrupted, status unknown)
- Fable (presumed uncorrupted, status unknown)
- When regenerating, Nephrite briefly assumed a humanoid shape – presumably reflective of her original form.
- It is unknown how many Corrupted Gems were Homeworld Gems and how many were Crystal Gems.
- However, it can be assumed that the majority were Crystal Gems due to not knowing about fleeing Earth.
- Some Corrupted Gems such as the Worm Monster and Nephrite were shown to have the urge to eat. The reasons for this are unknown but it was possible they did not gain sustenance from their gemstones as other Gems did.
- As shown by Nephrite and her crew it was possible for Corrupted Gems to be peaceful and even retain some aspects of their former personalities as Nephrite and her surviving crewmates retained their bonds with one another.
- As shown by the two Northern Gem Monsters from "Gem Hunt", Corrupted Gems were capable of feeling fear and their behavior indicates they may have a strong fight-or-flight instinct. This suggests that Corrupted Gems were not innately violent or hostile but instead possessed a mentality similar to a wild animal; attacking and/or fleeing from perceived threats. This may also explain Nephrite's passive behavior towards Steven and the Crystal Gems after reuniting with her crew despite being corrupted as she no longer saw them as a threat as she did in "Gem Glow".
- In "Monster Buddies" and "Crack the Whip" it was shown that Corrupted Gems could in a sense be tamed though with varying results. In "Monster Buddies", Steven was able to befriend and bond with the regenerated Nephrite. In "Crack the Whip", Jasper managed to tame the Corrupted Gems she captured in "Gem Hunt" through the use of intimidation and physical domination. While seemingly effective at first due to her method's cruelty the two Gems lacked real loyalty as they followed her out of fear of her and abandoned her if given the chance as shown in "Crack the Whip" and "Earthlings".
- Unreleased Corrupted Gems can be seen on Guy Davis' Tumblr such as the Stinger, the Fist Chest, and the Shell Back.
- Being poofed or put into an object can save a Gem from being corrupted by the Corrupting Light. It is unknown whether being trapped in an object or being poofed in general is what saved Lapis.
- It is revealed in "Earthlings" that corrupted Gems are capable of fusing with regular Gems. However, this will cause the uncorrupted Gem to become corrupted once the fusion is ended (as shown by Jasper's corruption). It is currently unknown if Corrupted Gems are capable of fusing with other Corrupted Gems.
- It is implied that Gems of the same type have the same corrupted form, as seen with Jasper, Biggs Jasper, and Ocean Jasper, both of the Water Bears, and Nephrite and her crew.