Max goes through one of the most emotional arcs of any character this season. Cursed by Vecna, Max is forced to relive some of her greatest regrets and traumas, including everything that happened with her stepbrother, Billy, and she barely escapes after her friends figure out that music can break (or at least delay) Vecna's trance.
In the end, that connection with Vecna proves pivotal to the final battle, where she uses the bond to try to lure Vecna into their trap. It works, but it also kills her — until Eleven mind-travels to her and is able to resurrect her. Still, it's not all sunshine: Max ends the season comatose in a hospital, with no word on when or if she'll wake up.