One of D&D’s greatest villains, Vecna 

Eleven's power returns after waking up from a dream about her past in Hawkins Lab

Steve being dragged into the water gate and millions of flying monsters trying to feed him

The scene where Eleven explores through her memories and the identity of 001 revealed

Max visiting Billy's grave and her expressing the guilt she feels

Max encounters Vecna is the epic scene of all in the Season 4