Corrupted Gems

"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."

Corrupted Gems, also known as Gem Monsters, are Gems who have become corrupted, assuming a monstrous form. One of the main missions of the Crystal Gems (about their protection of humanity) is to defeat and contain corrupted Gem monsters, and hopefully cure them.

Cause
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 an unknown light that corrupted any Gem it came into contact with. In "Monster Reunion", the Centipeetle Mother described it as a "song" and remembering it seemed to be what triggered her to revert.

Description
The appearance of the Corrupted Gems vary greatly with different Gems. Although, in "Monster Reunion" multiple Centipeetle Mothers can be seen, hinting at the possibility that like Gems will take on the same corrupted forms. As the bodies of gems are mental projections, the bodies of corrupted gems are a reflection of how damaged their minds are. With forms ranging from slightly humanoid, to monstrous, and some not having a physical body.

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.

Healing
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 currently no known way for un-corrupting Gems.

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.

Show:

 * 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

Steven Universe

 * Obelisk (comics)
 * Rainbow Cloud Monster
 * Snowbeast
 * Slug Monster
 * Plant Monster
 * Invisible Manta Ray
 * Clock Tower
 * Unknown Giant Bird
 * The Perils of Pweepwee

Steven and the Crystal Gems

 * Glass Ghost

Trivia

 * 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