Corrected entry: Throughout the movie we are presented with several different views of what the mansion looks like. At the beginning when Loomis plays it, later when the group does, and at the end when they finally enter the mansion, we are given 3 totally different mansions.
Corrected entry: When the Boss's men come to get Slevin, he already has some marks on his face from being punched in the nose. But when he is in the car with the Boss's men (after one of them had broken his nose again), the marks on either side of his nose have gone, but are back when he meets the Boss.
Corrected entry: In both scenes where Bruce Willis comes down the elevator thing in the car garage (in the regular storyline, and the retelling later), he shoots one of the bookies in the back. The camera angle shows the shooting happening with the car in view. It is plain to the eye that the driver's side window looks already shattered both times.
Corrected entry: As Slevin is walking down the hallway to The Fairy's apartment, his hair changes between shots. It goes from sticking up to slicked down to sticking up and back to slicked down again.