The Stranger Things season 4 trailer introduced a terrifying new monster, unlike anything seen in the show before; and it's likely this is the creature referred to in episode titles as «Vecna.» Every season of Stranger Things has upped the ante, with the Hawkins kids confronting threats of ever-increasing scale. The trailer for Stranger Things season 4 promises this trend will continue, introducing a monstrous new creature.
Unlike other monsters from the Upside-Down, this one is humanoid in appearance; it could well be the Upside-Down's equivalent of a human, or simply a person who was stranded in this dangerous realm some time ago and has been transformed. The monstrous being is shrouded in shadow, surrounded by sinewy tentacles reminiscent of the Mind-Flayer, and it seems to move with grim and inexorable purpose. Mirroring Stranger Things' Dungeons & Dragons themes, the dialogue over its first appearance ties to the board game idea; "You have lost."
Related: Why Stranger Things Uses A Journey Song In Season 4's Trailer
Visually, this creature corresponds with a monster from Dungeons & Dragons lore named Vecna — a creature mentioned in the episode titles for Stranger Things season 4. In the game's lore, Vecna was a wizard who sought dark magic and gradually transformed himself into an immortal creature known as a lich; his worshipers further encouraged his ascension to become an actual deity. Vecna granted his lieutenant Kas a sentient blade to act as his agent, but it persuaded Kas to turn on his master, leading to Vecna's apparent destruction. He left behind only two magical artifacts — his hand and his left eye, imbued with powerful dark magic. Curiously, most of the lore surrounding Vecna was established after 1986,
Read more on screenrant.com