I’ll probably make even longer extended posts at some point to better flesh out my points. But we got this for now!
Nancy is a Chimera: A distinctly female monster from Greek mythology. A creature born from Typhon, a child of Chaos, a chimera has the body and head of a lion, a second head of a goat, and a venous serpent for a tail. It’s known to be a ‘man-eater’ and is seen as a very powerful force in the stories it shows up in. However, chimera also appeared on many shields and crests, meaning to some degree the chimera also represented protection from foes and evil; a guardian of sorts. Being both a powerful and dangerous force but also a protector of evil seems to be pretty Nancy coded to me.
Jonathan is a Hippogriff: Said to be born of a Griffin and a mare, Hippogriffs has the front half of an eagle and the backside of a horse. Invented by an Italian poet, the Hippogriff is often viewed as a symbol of love itself and duality. In Jonathan’s case, he being a symbol of love is perfect as he (as well as all the Byers do) loves others with his whole being.
Steve is a Kirin: Steve is more often enough the peacekeeper and personal guard of the party. The beautiful and rare Japanese creature with the body of a deer, head of a dragon, and mane of a lion, Kirin are often referred to as Japanese Unicorns and really embodies Steve. They’re gentle creatures, known to not even hurt blades of grass when they walk, but are often fierce when they are protecting things they care for. They’re often seen as beacons of justice in Japanese folklore. Pretty much Steve ‘the Hair’ Harrington to a Tee.
Eddie is a Manticore: Another man-eater beast that is viewed more malevolently than the chimera is. Traced back to Persian and Indian roots, the manticore is beast with a lion’s body, the head of a man, and the tail of a scorpion. It was often depicted in Greek and Medieval mythos, the ladder using it as a representation of the devil. It’s also a creature quite popular in DnD oddly enough. While Eddie isn’t a beast by any stretch, the people of Hawkins see him as one. I’d say the leader of Hellfire Club would be best as Devil-like creature who was treated unfairly based on appearance alone.
Robin is a Puca: Puca are shapeshifting Celtic fae that love to stir up trouble but are also known to be helpful if willing. By accounts, older tales have Puca be characterized as much more bloodthirsty and dark whereas more modern tales have them mischievous at the very least or have them as helpful, luck bringers. I see Robin as a more modern Puca; a mischievous but helpful spirit that can be quite attentive to those she cares for.
Vickie is a Phoenix: With her fiery red hair and her nursing, picking a Phoenix was easy for Vickie. Traced back to Egypt and Greece for its earliest depictions, Phoenix are known most for their immortality, connection to death and rebirth, and symbolizing the cycle of life. Phoenix are also known for their healing properties and connection to fire. It’s pretty easy why it’s a good fit for Vickie.