"The Series Finale" of WandaVision kicks off with Agatha Harkness making it clear she wants the Scarlet Witch's power for herself, and it seems that taking the abilities of other witches is kind of her "thing" (explaining what happened to her coven and mother during that flashback to the 1600s). Wanda Maximoff attempts to use her powers on her one-time nosy neighbour, but Agatha effortlessly absorbs them as the Avenger's skin blackens. White Vision soon interrupts their battle, and attempts to crush Wanda's skull before the Hex Vision stops him. An epic battle ensues, all while Monica Rambeau - who is being held prisoner by "Pietro" - watches on.
Director Hayward taunts Jimmy Woo (who manages to nab a cell phone), and back in Westview, Agatha reveals she has the Darkhold, and that the Scarlet Witch is both more powerful than the Sorcerer Supreme and destined to destroy the world. The villain proceeds to release the minds of everyone in the town; they hate Wanda for what she's done to them, and make it clear they'd rather die than remain under her control. This causes her to lose it, and Wanda starts strangling them all with her powers before regaining her senses. Monica, meanwhile, learns that Pietro is really Ralph Bohner, a wannabe actor who lived in the house Agatha stole in order to pose as Agnes. Monica overpowers him, removes that necklace, and he regains his senses. Unfortunately, that's the last we see of him!
Wanda takes the Hex down so everyone can leave, but Vision, Tommy, and Billy start disappearing House of M-style. They can't live outside the reality Wanda has created, but Agatha will help them live on in Westview providing Wanda gives up her powers. The hero restores the Hex, and the family returns to action; Vision continues to battle White Vision, and Billy and Tommy take on the S.W.O.R.D. agents while their mom attempts to stop Agatha once and for all. Monica uses her newfound powers to save the kids after Hayward attempts to gun them down, and Darcy shows up just in time to stop him from escaping by driving the truck she and Vision stole into his vehicle. Surprisingly, the two Visions talk, concluding that neither of them are the true Vision, yet both somehow are. The Hex Vision restore's the original's memories, and he says only, "I am Vision" before flying off to parts unknown.
Wanda attempts to play mind games with Agatha, but ultimately concludes that the only way to beat her is to give the villain what she wants. Agatha takes great delight in revealing that the spell Wanda cast can't be changed, and that both her and her family will die. Wanda, however, has created some protection runes of her own, leaving Agatha powerless. Finally embracing her abilities, she becomes the Scarlet Witch, much to her foe's horror. Back on the ground, Agatha warns that Wanda has no idea what she's unleashed, and insists she'll need her help. The Scarlet Witch says that may well be true, but punishes Agatha by trapping her in her "Agnes" persona, saying she knows where to find her should she be needed.
The Hex comes down, and Wanda and Vision head home with the twins. After putting them to bed, they head downstairs together for one final goodbye as the Hex quickly closes in on them. Wanda reveals that Vision was created from the part of the Mind Stone that lives inside her, and he's her sadness, hope, and love. They ponder meeting again down the line (he hasn't mentioned the fate of White Vision, it seems), and he vanishes in front of Wanda, as does their house. The townspeople look on at Wanda in hatred, but she says one final goodbye to Monica as Jimmy and the FBI close in before vowing to understand her powers, and flying out of Westview as the Scarlet Witch.
There are also two post-credits scenes, and you get read full recaps of the both by clicking here.