Back to the Future
When Marty travels back to 1955 the name of the mall changes from Twin Pines to Lone Pine Mall. They even took away one of the pine trees on the sign. This movie is full of small details between timelines that you'll only catch upon rewatching. Zemeckis left no stone unturned in creating the perfect world for Marty McFly to explore.
Iron Man 2
The little kid in the mask that Tony Stark saves in Iron Man 2 actually grows up to be Spider-Man. Tom Holland's addition to the Avengers franchise portrays him as Tony Stark's apprentice. He teaches him the ins and outs of superhero-ing and trains him to be a successful crime fighter.