4. Engine explosion in Black Widow
When Black Widow was first released in theaters and Disney+, this particular scene made headlines for all the bad reasons. Superhero movies usually have few practical sets and, instead, are filmed against a green screen. Unfortunately, that can become evident in some sequences like the airport fight in Captain America: Civil War or the Quantum Realm scenes in Ant-Man and the Wasp: Quantumania. However, this was particularly obvious when Yelena Belova blew up a sky base's engine in Black Widow.
This scenes screams "GREEN SCREEN" in all caps. But if that wasn't enough, then the way Yelena is thrown away by the explosion's ripple effect is the cherry on top. Granted, what follows this not-so-good CGI moment is an exhilarating free-falling sequence that looks really good. But that doesn't take away from the fact that the event that set it in motion is considered to be one of the worst MCU VFX moments by fans worldwide.
3. Bruce Banner's floating head in Infinity War
For a movie as crowded with many different superheroes and action scenes as Avengers: Infinity War, its VFX holds up surprisingly well almost 99% of the time. That other 1% however... it's maddening.
Thor making an entrance in the battle of Wakanda near the end of the movie is one of the highlights of Infinity War as a whole. So we definitely could've done without that one poorly done shot of Bruce Banner opening the helmet of the Hulkbuster suit and telling the bad guys they're screwed now. The CGI in this single moment is so bad it distracts from an otherwise perfect sequence.
The movement of Bruce's head doesn't match the one from the Hulkbuster suit at all, so the former looks like it's floating inside the metal armor. This one little moment goes on to prove that the devil is in the details when it comes to creating movies, but it was nowhere to be found in this shot.