Monsters University

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I watched MU not too long ago. I remember before seeing the movie, I saw a street ad and a TV spot.
The TV spot showed Sully playing a Prank on Mike where he stuck a bunch of square mirrors onto him so he could be the disco ball of the party he was having at his house. The Street ad showed Mike taped to the wall by Sully.
In the final movie, there was a short rivalry between the two, but it is only in competition, and they get over it sooner.
What most likely may have happened is that the movie was originally going to have Mike and Sully as enemies and build up their friendship over time, but they encountered a problem and has to change the movie's course.

Thoughts?