She resembles a large crab. She has two large claws and six legs. On the top of her head, she has four small horns and in the center is one large spike. She has only one eyeball, and her iris appears to be the gemstone. She is only seen through Ronaldo's night vision camera, therefore the actual color of her shell is unknown. In the palette seen, she appears to be a dark teal color, although she could be orange and white, like her minions. She has two mandibles on her front acting as a mouth.
In her uncorrupted form, she has red, tan, and white coloring. She appears to wear a helmet with four spikes on top and a short bobbed hairstyle. She has one large eye and one pointed tooth. She has broad shoulders and still possesses a large claw on her right arm, with her left arm having four pointed fingers.
The Crab Gem Monster resembles Gohma from the Zelda series, particularly in how she seems to use her claws to help protect her eye, which is her weak spot as well as her ability to spawn smaller versions of herself.
The Crab Gem Monster is similar to Nephrite in her corrupted state, and the Gem Cave Creature, in the sense that she is able to summon smaller versions of herself.
She is currently the only character to have less than five fingers on each hand, having only four on her normal one.
Even though Quidd; who has access to the model sheets, has listed her as "Aventurine", it is unknown whether or not this information can be factual as it has not been confirmed in-show, or by the Crewniverse.