Cluster Gems (Canon)

"They were forced together...! They were forced to fuse!"

"Cluster Gems", also known as Gem Mutants and Artificial Fusions, are forced fusions of former Gems. They were supervised by Peridot and other Homeworld Gems created to serve as prototypes for the real Cluster. As of "Nightmare Hospital", new Cluster Gems have started emerging and become increasingly mobile and violent. These experiments were created in the Kindergarten.

Appearance
In general, Clusters take the form of limbs joined together to other appendages. The limbs are of mismatched colors, such as dark and light blue, rust, violet, olive green, mint gray, pale green and dull yellow, indicating that they originally belonged to different Gems.

"Marble Madness"
The Cluster Gems make a semi-hidden cameo when Peridot is accessing the Facet Five control room.

"Keeping it Together"
Steven and Garnet encounter Cluster Gems in the Kindergarten, the Hand Cluster and six smaller Cluster Gems. The appearance of the Clusters is so horrifying to Garnet that she becomes unstable to the point where she almost un-fuses. Ruby, through Garnet, states she believes the Cluster Gems were created as punishment by Homeworld for The Rebellion. The Cluster Gems are eventually "poofed" by Garnet and currently reside within one of her bubbles in the Burning Room.

"Nightmare Hospital"
Two Clusters are sighted across roads and taken to Dr. Maheswaran's work place, mistaken as victims of car accidents and treated by doctors at the Hospital. Later, they break into the halls and try to attack Steven, Connie and Dr. Maheswaran, only to be poofed by Connie with Rose's Sword and then bubbled by Steven.

"When It Rains"
Peridot and Steven are assaulted by several of them when attempting to escape the Kindergarten before Steven forms a bubble and they are rescued by the Crystal Gems. This is the second time where the Cluster Gems are shown to have facial features (i.e., mouth, eyes); the first time being "Keeping it Together".

Trivia

 * Coincidentally or not, if one excludes Hand Cluster's thumb (which is covered by a boot), it has a glove covering every finger but the middle, while Garnet has a glove covering her middle finger.
 * The blue "leg" off to the left of the Hand Cluster appears to have the same boots as Amethyst and Ruby.
 * There appears to be no red Gem Shard in the Hand Cluster, despite the red leg and arm present in it.
 * The silhouettes of the Hand Cluster members have traits similar to other Gems on the show. For example, their hairstyles are similar in appearance to that of Pearl's haircut from the Pilot.
 * When the Hand Cluster's gem was sent to the Burning Room, its gem reshaped itself to appear like the Centipeetle Mother's gem.
 * This was later confirmed to be an animation error by Matt Burnett via Twitter.
 * Each of the Hand Cluster's eyes has a defined plica semilunaris on either side of it, not seen elsewhere on eyes in the show.
 * In "Nightmare Hospital", it is mentioned that they have no vitals or heartbeat, a fact that may also pertain to regular Gems as well, given their fluid physiology.
 * In the episode "When it Rains" two Cluster Gems with actual heads, mouth and eyes are among the group attacking Steven and Peridot.

Cultural References

 * Clusters share many similarities to Frankenstein's monster from the famous film adaptation of Mary Shelley's novel of the same name.
 * Both are made out of body parts of different deceased individuals, acquired via grave robbing.
 * They are unnatural creations which were created through scientific means.
 * Both are represented as tragic, yet horrifying figures.
 * The malformed appearances and multi-limbed forms of the Cluster Gems give them a striking resemblance to the Necromorphs from the Dead Space series.
 * Their grotesque amalgamations of body parts also bear resemblance to John Carpenter's The Thing, as well as its 2011 prequel, which does show arm-based creatures.
 * The two-headed Cluster Gem resembles the Charger in the Left for Dead video game series in terms of anatomical design.
 * The Hand Cluster's cloth makes it resemble a mummy.
 * The rock cylinders used to hold the immature Cluster Gems resemble rock core samples.

Gemology

 * A cluster of gemstones is a result of gems that fuse together due to extensive pressure from being underground. In most cases clusters are usually fusions of the same gemstone; however, in very rare cases, it is possible for clusters to form from different gemstones.