"The Slinker" is a corrupted gem that is the main antagonist of the Steven Universe episode, "Reformed".
"Reformed"
The Slinker is a plant-like corrupted gem with root-like tentacles and a square gemstone inside it. The Crystal Gems detected in Amethyst's room of the Crystal Temple. It slithers and scurries in Amethyst item piles and even manages to destroy her physical form multiple times. When it tried to consume her gemstone, Garnet knocked it into another item pile, never to be seen again. It's still at large.