Originally, Professor Hulk was supposed to have been introduced in Infinity War, but it was decided that his arc would function better if it was spread across two movies. Co-writer Chrisopher Markus said, “There was a time when Banner became Smart Hulk in the first movie. It was a lot of fun, but it came at the wrong moment. It was an up, right when everyone else was down.” Even after switching the transformation to Endgame, the writers struggled with how to make the reveal. They considered inserting a scene in Bruce Banner’s lab, but instead chose the more comical reveal at the diner, with Ant-Man.
Thor’s Big Lebowski
Out of all the characters crammed into Endgame’s final cut, it was Thor who underwent the most dramatic transformation. Perhaps taking too much of a liberty with Chris Hemsworth’s comedic appeal, we were shocked to see that the five-year time jump hadn’t been too kind to the formerly fighting-fit Thunder God, taking him down a path of depression, alcoholism and obesity. Iron Man calls him "Big Lebowski", and the comparisons to Jeff Bridges' The Dude are frighteningly accurate – but it nearly didn’t turn out this way. In fact, writers Markus and McFeely revealed Thor nearly took on the role of vengeful killer in place of Hawkeye
Tony Stark’s vision
The Russos, in an appearance on the HappySadConfused podcast, said that a scene showed Tony interacting with a teenage Morgan (played by Katherine Langford) immediately after snapping his fingers, similar to how Thanos went into the metaphysical world after he’d snapped his fingers. “There was an idea that we had that Tony was going to go into the metaphysical way station that Thanos goes in when he snapped his fingers. And that there was going to be a future version of his daughter in that way station,” Joe Russo said. The scene between Iron Man and his daughter was shot, but cut out after test audiences expressed confusion.