The Scarlet Witch is coming!
In today's episode of WandaVision, we learn that Wanda Maximoff has always had magical powers, with her exposure to the Mind Stone simply switching on what was already there. Later, we learn that it's actually "Chaos Magic," and Agatha Harkness reveals Wanda is, in fact, "The Scarlet Witch."
In the comics, Chaos Magic is the name of a magic so powerful that it was thought to be non-existent by even the Sorcerer Supreme himself. This magic can manipulate, warp and reconstruct the very fabric of existence and reality to the user's very whims and bring about total destruction to the cosmos. So, that definitely goes some way in explaining how Wanda changed Westview!
During a flashback to the Avenger's first exposure to the Mind Stone, we learn that Wanda had a glimpse into her future. As you can see below, she's shown what is quite clear a 100% comic accurate take on the Scarlet Witch's costume. That explains where she got the inspiration from for her Halloween outfit, and the tease on one of those character posters with Wanda's new look.
With it looking increasingly unlikely that there is a secret big bad like Mephisto or Nightmare pulling the strings, it seems WandaVision will instead be about Wanda becoming the Scarlet Witch.
Honestly, that's not a bad thing, but how it ties into the MCU's future obviously remains to be seen!