Tongue Monster

The Unknown Corrupted Gem is a corrupted Gem that first appeared in "Kindergarten Kid".

Appearance
The Unknown Corrupted Gem is a bipedal, avian-esque Gem, with two long dark green legs which lead into an orb-shaped and teal colored body. On either side of its head are a set of three small eyes with white scelera and lime-green irises. Its has a large mouth with fang-like teeth and a set of three gray tongues it often undulates when calling out while bobbing up and down. Its gem is located on the center of its nose and is a mixture of blue-green, grey, and brown colors that are different on each facet.

Abilities

 * High Speed: It can run at extremely high speeds, making it immensely difficult to capture, even when trying to grab onto it such as when Amethyst latched onto it using her whip.
 * Enhanced Strength: It is capable of towing gems like Amethyst and Peridot behind it while still running at maximum speed, and was easily able to lunge onto Steven and attack him using its talons.
 * Intelligence: It was capable of outsmarting Peridot and Steven's plans, and even inadvertantly caused Peridot to get crushed by a massive boulder through its curiosity.

"Kindergarten Kid"
The Unknown Corrupted Gem was the main antagonistic force in the episode. It was left in the Beta Kindergarten after Jasper had been corrupted and poofed as a remnant of her army which was being rounded up by the Crystal Gems. When Pearl, Garnet, and Amethyst were incapable of capturing it, Peridot and Steven went out to hunt it down. Peridot attempted to outsmart it with her various "Peri-plans", however despite her and Steven's best efforts it managed to cause each of their plans to backfire. Steven then suggested that Peridot should think like the Corrupted Gem. Eventually Peridot and the Corrupted Gem fell of a cliff, which Peridot survived due to her innate durability, while the Corrupted Gem was poofed by the force of the fall. Peridot then bubbled its gem which end up being sent to The Barn instead of the The Burning Room as Peridot considers the barn to be her home.

Trivia

 * It resembles the small figurine Steven had in his room which he showed to Holo-Pearl in the episode "Steven the Sword Fighter", which in turn parodied Sonic the Hedgehog, who is also known for his remarkable speed.
 * It parodies a well-known Looney Tunes character, the Road Runner, who was known for his antics alongside Wile E. Coyote.
 * Like the Road Runner, it has avian like characteristics, high speed, and also makes gurgling sounds.