The Gem Cave Creature appears as a gigantic brittle star, with a massive disk and short arms. The upper portion of its disk appears as a giant mound of turquoise colored crystals with multiple geometric facets. The lower half of the disk is colored dark turquoise. The arms are joined near the middle of the disk and taper to a point outwards, they are of a darker shade of turquoise. The ventral side of the disk contains a drill-like apparatus that can unfurl to reveal five turquoise colored arm, and appears to have fingers, that surround a mouth. The dorsal side of the disk houses multiple Drill Parasites that furl themselves to form spike-like protuberance that the Gem Cave Creature can launch.
The Gem Cave Creature has the ability to burrow underground, by using the drill underneath its disk. It can unfurl its drill to produce five more arms to enhance its fighting capabilities. Its arms also have the ability to stretch to great lengths, as seen when it was fighting Garnet. Its body is presumably durable enough from attacks, as Garnet had to get close to it and hit its weakest point, which was its mouth. It can also launch multiple spikes from its disk, which can unfurl and become Drill Parasites that can aid it in battle.
The Crystal Gems were attacked by it, which Garnet successfully managed to defeat, and proceeded to bubble its gemstone.
- In "Ocean Gem", it's revealed that monsters, which left behind gemstones upon defeat, were previously Gems that became corrupted in some unknown manner.
- It is the second corrupted gem shown with the ability to create offspring.
- The Gem Cave Creature resembles Brittle Stars more than a Starfish.
- Brittle Stars (Ophiuroids) resemble true Starfishes/Sea Stars (Asteroids), but the main difference is that brittle stars have a distinct central disc and five radiating slender, highly flexible arms. The arms are solid and not hollow like the sea stars, whose central disk and arms are inconspicuously parted.