While it is not known to evolve into or from any other Pokémon, Zygarde has the following three Formes:
Zygarde 10% Forme, one of the Formes introduced in Sun and Moon
Zygarde 50% Forme, the Forme introduced in X and Y
Zygarde Complete Forme, one of the Formes introduced in Sun and Moon
Along with these Formes are two basic components of Zygarde: Zygarde Cores, which act as the brains of Zygarde, and Zygarde Cells, which compose Zygarde's Formes and cannot think. Neither Zygarde Cores nor Zygarde Cells can use moves or are useful in battles by themselves. Both of these components were introduced in Pokémon Sun and Moon. They are stored inside the Zygarde Cube.
Zygarde 50% Forme was introduced in Pokémon X and Y. Zygarde Cell, Zygarde Core, Zygarde 10% Forme, and Zygarde Complete Forme were announced in the October 2015 issue of CoroCoro magazine. The remaining forms were introduced in Pokémon Sun and Moon. Prior to their appearance in Sun and Moon, Zygarde's other forms played an important role in the anime's XY&Z arc.
Zygarde is a Pokémon whose form depends on the percentage of its Cores and Cells gathered together. A Zygarde Core is the brain of the Zygarde. It is a small, green Pokémon with a gelatinous body. It has a large, round head with a beak-shaped protrusion on the front, a thin, hook-shaped tail, and a red hexagon suspended in its body. Within its head is a single eye with a black pupil; beside this eye is another white oval that may be a second eye. As seen in the anime, Zygarde Cores are capable of absorbing sunlight to regain their strength and can speak telepathically. Zygarde Cells make up every other part of Zygarde and appear nearly identical to the Zygarde Core. Unlike the Core, it has a flat body and head. It has a green pupil, a simpler, unhooked tail, and has a darker green, more elongated hexagon within its midsection.
Cores and Cells do not have the power to battle alone and can only fight when combined to form Zygarde. The Cores have their own will and are sometimes able to act on their own, while the Cells form the rest of Zygarde's body and are only able to act on the Core's orders.
Zygarde 10% Forme has a relatively small canine body. It is primarily black with a green collar and a leash-like extension on its neck. Additional green markings include: two hexagon markings on its chest, a small hexagon over each eye, the area around its mouth, and its front left paw. There is an elongated, red hexagon marking attached to the collar marking. Its eyes are white hexagons with no discernible pupils and there is a thin, white line on its forehead. On each of its legs are hexagonal extensions: two on the back of each elbow, one behind each knee, and two on each hip. One of the hip extensions is longer than the other on each hip. This form has razor-sharp teeth and is skilled at close range combat. It is also capable of running at speeds greater than 60 miles per hour (100 kilometers per hour).
Zygarde 50% Forme has a serpentine body with green and black markings. Most of its back, head, and neck are black, while the underbelly and the tip of its tail are green. Its eyes are made of four green hexagons, similar to an insect with compound eyes, and there is a thin, white line down the center of its face. Across the back of its neck is a large frill made of five long, flat protrusions that each have two small, green hexagons on them. There are three short tendrils on either side of its chest; they are black on the right and green on the left. Its tail also ends in five tendrils. It has many small, green hexagon markings on its body capable of glowing. This form of Zygarde is thought to monitor those who destroy the ecosystem from deep with its cave. Should the region's ecosystem fall into disarray, it will appear and reveal its power.
Zygarde Complete Forme has a large, humanoid body with a long tail similar to Zygarde 50% Forme's body. There are several flat protrusions around its head and triangular protrusions around its neck. These protrusions create a crown-shape. On its face are three white hexagonal marks: one in the middle of its forehead with a line through it and two that act as eyes. There are an additional five green hexagons on its face: four along the bottom and one in the middle of a short protrusion on top. Each shoulder has two serpentine wings protruding from it. The wings all have an undulating pattern and a hexagon near the tip: blue on the right side and red on the left. There are multiple white protrusions on its body: three on each hand acting as claws, one on each knee, and one and the front of each foot. Additionally, there are green hexagons surrounding its wrists and two under the white protrusions on its knees and feet. Its abdomen has a vertical, hexagonal pattern with a thin, white line on either side. Across its chest is a thin, zigzagging opening that fades between five colors: red, orange, white, cyan, and blue. The chest can open, revealing five cores of each color. Above this opening are two large green, hexagonal marks.
Possessing all of its total cells, Zygarde Complete Forme is said to exceed both Xerneas and Yveltal in power. The opening on its chest can radiate enough energy to destroy anything around it. This form only appears to neutralize threats to the ecosystems.
A single Core acts as the brain for the 10% form. This allows it to take action separately from Zygarde's 50% Forme, which comprises its main body, for a short time. Zygarde Complete Forme contains separate Cores for each of its wings and its tail. In this case, each Core can make decisions and act independently of the others.
Zygarde debuted in Hawlucha Attack. It was first mentioned by Blue, who aimed to find it in order to stop the endless battle between Xerneas and Yveltal. It physically appeared at Anistar City, where it was sought after by Essentia, who aimed to capture it for Team Flare. When X and Y battled Essentia in order to retrieve Y's stolen Xerxer, Zygarde appeared before them and attacked before Essentia managed to successfully catch it.
Zygarde was later used by Essentia to battle X, Blue, and Blaine. After Emma was freed from Lysandre's control, she was about to order Zygarde to attack him, but he managed to take its Poké Ball, fully putting it under his control. Zygarde was later used to fight X's Mega Evolved team, but as the battle progressed, Emma noticed green blobs falling off of it. At that moment, Xerneas and Yveltal returned to their dormant forms, causing it to disintegrate, and X hit it with a combined attack from his team. This resulted in Zygarde exploding into millions of green blobs, and Lysandre began to fall. Soon after the battle ended, Blue and Blaine visited Sycamore and mentioned to him about seeing a little green silhouette after Zygarde disintegrated into the blobs. Sycamore revealed to them that similar green silhouettes, which he dubbed Zygarde Cells, were spotted in a faraway region as well, and sends Dexio and Sina to investigate them in Alola.
Zygarde 50% Forme or 10% Forme with the AbilityAura Break can be assembled into Zygarde 50% Forme with Power Construct using 100 Cells and Cores from the Zygarde Cube. Zygarde with Power Construct can freely switch between its 10% Forme and 50% Forme using the Zygarde Cube.
Zygarde 10% Forme may be based on Fenrir. The green leash-like object around its neck could be based on Gleipnir, the rope that binds Fenrir. Also, its left front paw has a different color from the others, being green instead of black, which is possibly a reference to Fenrir biting off the god Týr's right hand in reprisal for being bound by him. This Forme could also draw inspiration from Garmr, the watchdog that guards Helheim's gate. In appearance, Zygarde 10% Forme resembles a Doberman Pinscher.
Zygarde 50% Forme's appearance is based on a serpent in the shape of the letter Z. It may also draw inspiration from Jörmungandr, a sea serpent that encircles the earth, and Níðhöggr, a dragon that gnaws at the roots of Yggdrasil, the world tree. Its flat shape and wriggling movement may be inspired by the tsuchinoko, a Japanese cryptid, and its snakelike appearance may be inspired by nāga, a class of snake entities in South and Southeast Asian cultures.
Zygarde Complete Forme may be based on Hel, the ruler of Helheim, the realm of the dead in Nordic myth. The colors on Complete Forme's chest match the colors of the real-world flag of France, the country which inspired the region of Kalos. These colors also match the colors Xerneas and Yveltal. Design-wise, Zygarde Complete Forme resembles a humanoid giant mecha despite its organic basis; its light-up technological appearance, "transforming"/"combining" gimmick, and the face-like pattern on its chest are all tropes commonly used for fictional mecha.
Zygarde Cell and Zygarde Core may be based on cells as well as flatworms (specifically planaria) and single-celled organisms such as slime molds and members of Euglena. Some planarians' ocelli also resemble eyes, which may have inspired the designs for the Cell and Core Zygarde. The hexagons within them may represent a cell nucleus.
Zygarde comes from the letter Z. It may also be derived from ζυγωτός zygōtos (Greek for joined), zygote, garde (French for guard), midgard (Old Norse: Miðgarðr), or Sigurd.