Its body in its 50% Forme is shaped like the letter "Z" and appears to be a snake. It has a green top half and a black bottom with 5 Pillar-like shapes on its back. It has no arms or legs and has a various amount of scales on its body. Zygarde has two compound eyes and green shapes under them. It has a tail which is flat.
Zygarde is part of a legendary trio that include Xerneas and Yveltal, together spelling X, Y and Z, the last letters of the alphabet. They also happen to be the last Pokémon in the Mountain Kalos Pokédex.
Zygarde is the only Legendary Pokémon to have more than four formes.
Zygarde 50% Form is based off of a serpent in the form of the letter Z. Zygarde 10% Form is based off of a Doberman Pinscher on a green leash. Zygarde Cell and Zygarde Core are based off of cells and possibly planaria. Zygarde Complete Form is based on Hel, a Nordic goddess.
Zygarde's name has been derived from two words. "Z(ee)" responds to Z axis and "garde" is a French word meaning guard or protection. It is a part of Yggdrasil Trio.
Red Zygarde Core
Red Zygarde 10% Forme
Zygarde 50% Forme
Zygarde Complete Forme
Zygarde's 50% Forme as shown in the Pokémon Dream World