7. There's Something Strange About Strange
The theory that Mephisto is about to make his MCU debut is basically a meme at this point. It was a popular prediction throughout WandaVision and Loki, but because it didn't come true in either of those cases, the whole idea has become a bit of a punching bag within the MCU fandom.
But even though we've been burned multiple times, the Mephisto theories have ramped up again after the No Way Home trailer, with many fans guessing that Doctor Strange... is actually the devil in disguise. Cue the dramatic music.
Sure, that theory could be true - with all the crazy stuff that's happening in the MCU lately, it would be foolish to rule it out - but when the filmmakers go out of their way to feature a shot like this in their movie, it honestly just feels like they're baiting us.
So no, we aren't going to say that Doctor Strange is actually Mephisto in disguise, but we have to admit, something does seem off about the character's presence in the trailer. More specifically, there are a couple of occasions where he seems to be acting a bit hostile towards Spidey, whether he's trapping him in a load of train cars, or aggressively stating "be careful what you wish for, Parker."
So - jumping off our previous theory - what if one of the universes Peter finds himself in is an "evil Doctor Strange" universe, where he has to do battle with a dark variant of the Sorcerer Supreme?
The recent Doctor Strange episode of What If...? could've been designed to introduce fans to this concept, and this would certainly explain why Strange (who, incidentally, is wearing a dark version of his costume) seems to be chasing Spidey down in that gravity-defying train sequence.