Zygarde 50% Forme has a serpent-like body with a green and black pattern on it. There are black frills on the back of its head like a frilled lizard. Its eyes comprise four green hexagons like the compound eyes of of an insect. More green hexagons are on the front and back of its frills. These hexagons glow in certain patterns like a computer processing information. Its tail is flat and is black on top and green on the bottom. Its tail ends with five separate green tendrils. It is said to monitor the ecosystem, and if the ecosystem falls into disarray, it appears and reveals its power.
Zygarde Complete Forme is said to exceed both Xerneas and Yveltal in power, possessing 100% of its total cells. Zygarde only enters Complete Forme when the Zygarde Core believes it is outmatched.
Zygarde 10% Forme possesses 10% of its total cells, has razor-sharp teeth, and can reach speeds up to 60 mph.
Zygarde Core is a part of the mind of Zygarde. They are self-aware and can communicate via telepathy, monitoring the ecosystem around them. There are two Cores, one composed of a red hexagon and one composed of a blue hexagon.
Zygarde Cells make up Zygarde. They are unable to think and incapable of using moves.
Zygarde is the only known Pokémon that can learn Land's Wrath.
Origin
Zygarde 50% Forme's appearance is based on a serpent in the shape of the letter Z. It may also draw inspiration from both the Níðhöggr and the sea serpent Jörmungandr (also known as the Midgard Serpent or World Serpent). According to the Prose Edda, Jörmungandr is punished by Odin by tossing it into the great ocean that encircles Midgard. The serpent grew so large that he was able to surround the earth and grasp his own tail. Níðhöggr is the serpent from the Poetic Edda which resided at the bottom of the world tree Yggdrasill and gnawed at its roots. The patterns spread across Zygarde 50% Forme's body are very similar to ribose and deoxyribose molecules. Its tail is possibly based in shape on base pair codons, the essential building blocks of the DNA double helix.
Its 10% Forme appears to be based on Fenrir. In Norse mythology, Fenrir is a giant wolf forever growing. He was invited to stay in Asgard and was chained multiple times, but broke the shackles with ease. 10% Forme's razor sharp teeth may be an allusion to Fenrir biting off the hand of Tyr and his strength. The green scarf-like object around its neck could be based on Gleipnir, the rope that was able to bound Fenrir until Ragnarok. This form could also be based on Garmr, the dog of Hel and watchdog that guards Hel's gate. Appearance-wise, 10% Forme resembles a Doberman Pinscher.
Its Complete Forme is possibly based on Hel, the ruler of Helheim, the realm of the dead in Nordic myth. Along with Jörmungandr and Fenrir, Hel is a child of Loki. Given that both Fenrir and Jörmungandr were fated to die fighting against the gods during Ragnarok, it is possible that the Complete Forme is based on Loki himself, who also fights a god during Ragnarok and is killed. The colors on Complete Forme's chest match the colors of the flag of Kalos. The red and blue markings on either side may represent Yveltal and Xerneas as this form exceeds both of their powers.
Zygarde Cell and Zygarde Core are based on cells. Both look similar to flatworms, specifically the planaria. Their appearances resemble the wide body of the Tsuchinoko. The hexagons on them could represent the cell membranes of cells.
The order of Zygarde's 10%, 50%, and Complete Forme mirrors how powerful their counterpart is, with Fenrir being weakened by the gods to Hel/Loki being on equal-footing with the gods.
Name origin
Zygarde comes from the letter Z. It may be derived from ζυγωτός zygōtos (Greek for joined), zygote, and garde (French for guard), and zygōtos and midgard (Old Norse: Miðgarðr).