Fans theorized that Thanos's wrinkles in Infinity War hinted at a fight with Wolverine, which turned out to be baseless.
Speculation that Mephisto was the mastermind behind everything in WandaVision, despite the showrunner's denial.
The belief that an aerospace engineer cameo in WandaVision would introduce a major new character, which turned out to be anticlimactic.
The theory that Black Widow was pregnant with Captain America's child in Infinity War, which was debunked by established movie canon.
The anticipation of Venom appearing in The Amazing Spider-Man 2 due to a misinterpretation of a trailer shot.