The Gryncore is green and orange in color, and resembles a six-legged insect. According to Metroid: Samus Returns Official Guide, the Gryncore only has one eye, and is described as "door-gobbling", suggesting that this parasite somehow feeds off of the door. It possesses a sturdy shell that can only be penetrated with the Plasma Beam and Power Bombs. Once killed, the Gryncore drops many pickups and never respawns.
Gryncores are commonly found blocking access to items. While they are most commonly found throughout Area 5 (where the Plasma Beam is located), they are present in many other areas of SR388, including the Surface (blocking a Super Missile Tank), Area 1 (blocking an Aeion Tank, which is also blocked by crystals), Area 2 (blocking a Aeion Tank), Area 3 (blocking a Super Missile Tank), Area 4 (blocking a Super Missile Tank), and Area 7 (blocking the last two Omega Metroids).
An unidentified grass-like material grows in close proximity to doors covered with Gryncores. This material disintegrates when the Gryncore is killed, suggesting a symbiotic relationship.
- DOORS (pg. 26)
- "Like Gigadoras, Gryncores are well-armored and can take just about any beating. Missiles, Super Missiles, Bombs, etc., don't leave a mark. The only way to get around these green one-eyed door parasites is with the ultimate in beam weapons: The Plasma Beam. Against the Plasma Beam, a Gryncore doesn't stand a chance."
- Walkthrough - Gryncores?! (p. 39)
- "If you do venture to the upper part of the room, you find a door-gobbling organism known as a Gryncore. These and a small handful of other door-mounted creatures are scattered throughout SR388. Each of these door beasts has a weakness to a particular weapon and nothing else. To get through these doors, you need a lot more weaponry than you have currently."
- Walkthrough - The Plasma Beam and Gryncores (p. 144)
- "The Plasma Beam doesn't radically change your beam weapons aside from increasing the power. What it does that's of note is allow you to destroy the Green Door parasites known as Gryncores, which is quite handy for reaching new item tanks."
- The grass-like material seen near Gryncores bears a striking resemblance to a similar material seen hanging from platforms on Planet Zebes: Brinstar.