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Zygarde's 10%, 50%, and Complete Formes may be inspired in part by three children of Loki and Angrboða: Fenrir, Jörmungandr, and Hel. The order of these Formes may also reflect the relative power of their inspirations, Fenrir and Jörmungandr being below gods and Hel being on equal-footing with the gods.
Zygarde 10% Forme appears to be based on Fenrir. Its razor sharp teeth may be an allusion to Fenrir biting off the right hand of Týr. The green scarf-like object around Zygarde 10% Forme's neck could be based on Gleipnir. This Forme could also draw inspiration from Garmr, the dog of Hel and 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 the sea serpent Jörmungandr and the dragon Níðhöggr. Jörmungandr in particular is a classical example of an ouroboros, a symbol used to represent cyclicality. The patterns spread across Zygarde 50% Forme's body are very similar to ribose and deoxyribose molecules. Its tail's shape is possibly based on base pair codons, the essential building blocks of the DNA double helix.
Zygarde Complete Forme could be based off of Hel, the ruler of Helheim, the realm of the dead in Nordic myth. She is often depicted as a half alive and half dead being, which may have inspired Zygarde's theme of the balance between life and death. The uppermost section on Zygarde Complete Forme resembles a crown with jewels embedded within it, which may be a reference to Hel's title of Queen Hel in Bartholomeus saga postola. 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. The red and blue markings on either side of Zygarde Complete Forme may represent Yveltal and Xerneas, as this Forme exceeds both of their powers.
Zygarde Cell and Zygarde Core are based on both cells and flatworms, specifically planaria. Planaria and other similar flatworms are notable for their regenerative abilities, and will eventually form into multiple creatures if split apart. The fact that many Zygarde Cells make up a single larger creature may be in reference to this. Some planarians' ocelli also resemble eyes, which may have inspired the designs for the Cell and Core Zygarde. The hexagons within them likely represent a cell nucleus.