"You break the rules and become a hero. I do it, and I become the enemy. That doesn't seem fair." This is what Wanda says to Dr. Strange hinting a fight between them two, and we see an obvious fight of a glowing figure (Could be Captain Marvel or a Variant) fighting Wanda.
Destined To Be The Destroyer Of Realms
In the post credits of WandaVision, Wanda hears the voice of her twin boys, probably across the dimension. This is the sole reason Wanda could turn into an Evil Witch, to save & get her life back with her twin boys & Synthetic Husband from another universe & fulfill her destiny to become The Scarlet Witch: Destroyer Of Realms
But Why Wanda Goes The Villain Road
The Zombie Strange we see in the trailer could possibly the main villain causing all the chaos, he is dead and a sorcerer on top of that. The other Sinister Dr. Strange seems to be a misdirect since he was redeemed in the animated "What If...?" series. Major cameos and twists are actually from the "What If..?" series.
Doctor From The Zombie Land
This could be the actual main villain as the trailer hinted his existence and misdirected fans with other versions of strange himself. "The Nightmare" is from the 'Dream Dimension' and one of the biggest foes of Dr. Strange. As we hear Strange in the begninig "Every Night I Dream The Same Dream And Then The Nightmare Begins"
Villain Hidden In The Dreams
There are more heroes than villains in Doctor Strange 2. America Chavez, a hero across the univers who can punch through air and open star shaped portals, we see her falling together with Dr. Strange and taking him into another dimension instantly to save themselves. She is the first Lesbain Hero.
An LGBTQ Super Hero
We also hear and see the bald head of Charles Xavier when Dr. Strange is handcuffed by Ultron like robots and put on a trial in front of the Illuminati, we can expect to see an Iron Man Variant as he's one of the Illumiinatis along with Charles Xavier, Dr. Strange, Black Bolt and Namor of The Lost Atlantis.
Marvel Set To Introduce The Illuminati