The Multiverse of Madness trailer definitely wants viewers to think of Doctor Strange as a potential villain: he's arrested by Mordo, taken to face what appears to be the Illuminati, and at the end there is a shot of a panicked, imperilled Wong. The Doctor Strange in the Multiverse of Madness trailer could be an amalgamation of Nightmare and a Strange variant, and earlier shots of Strange's dreams or visions would fit with the villain. It is possible that one of the Scarlet Witches in the Doctor Strange 2 Super Bowl trailer is the real villain of the movie, and has caused the madness in the multiverse as a means of either desperately trying to find her children, or as a cause of revenge.
The idea that Nightmare is Doctor Strange in the Multiverse of Madness' villain and that Doctor Strange has been trapped in the Nightmare World of the Dream Dimension is supported by that line.
In one scene with Doctor Strange, she says, "You break the rules and become the hero", which seems to indicate that she will be seen as the villain of Doctor Strange in the Multiverse of Madness, regardless of her true intentions.
The Doctor Strange in the Multiverse of Madness trailer raises a lot more questions than it answers: there are hints of the Illuminati, multiple versions of Doctor Strange, and Captain Carter in the poster. He would fit with the multiverse collapsing and allowing various worlds to bleed into one another, as well as fitting with multiple lines in the trailer: "every night I dream the same dream, then the nightmare begins." It's more likely that Doctor Strange isn't the villain and is, at worst, grossly irresponsible for whatever actions have led to this, whether that's from No Way Home or something new, like reading the Darkhold.
The Doctor Strange 2 trailer hints at a bigger villain than Gargantos, which may be a new name for Shuma-Gorath, or an amalgamation of the two. The full Doctor Strange 2 trailer, which was released during the Super Bowl with a new TV spot, suggests that nothing is off the cards as far as this movie is concerned. Things are going from bad to worse for Doctor Strange after he inadvertently opened up the multiverse in Spider-Man: No Way Home.
The Super Bowl trailer raises the possibility of a villain named Nightmare in Doctor Strange in the Multiverse of Madness. It is possible that Wanda is the threat they have convened to deal with, and that is the "truth" they need to tell Doctor Strange. Wanda comes off as annoyed and threatening in the scene, and her being seen as the enemy suggests she is setup as Doctor Strange in the Multiverse of Madness' villain.
The Spider-Man: No Way Home's post-credits scene was teased in the first Doctor Strange trailer. The biggest question of all is who is Doctor Strange in the Multiverse of Madness' villain? This was something WandaVision's post-credits scene hints at, with whispers of her children being held in the Dream Dimension, and that could be a link between all the characters in Multiverse of Madness. With the return of Professor X in Doctor Strange 2, and the fact that he is in the first trailer, there are likely even bigger surprises in store.
The trailer supports the theory that Doctor Strange is the villain in the Multiverse of Madness.
There is a chance that Doctor Strange is the villain in Doctor Strange 2. Given there are multiple versions of Strange, it's possible that one could be villainous and cause all of this. There were signs that Wanda was reading the Darkhold in order to find her children. While the ending of WandaVision seemed to show her getting back to her old self, the truth was that she was reading the Darkhold. Doctor Strange could be the villain in Multiverse of Madness because he has been interfering with forces beyond control. Doctor Strange 2's villain, Nightmare, has been rumored for a long time, despite no firm confirmation.