Revealing mistake: When Walters is electrocuted, the kettle on his head is not resting on it but is fixed on the grid behind him, as to prevent it from falling off. Since Walters moves his head slightly, so should the kettle.
Revealing mistake: The cloud which drenches Topper at the railroad station casts no shadow over him.
Revealing mistake: When Topper is fighting the Thai Fighter, they break the ladder that sends some people falling down. Before the shot cuts, you can see the guy with the pink shirt falling, and he has a dummy attached to him. This is not the same as other dummies who are obviously meant to be noticed (like the guy holding the "John 3:17" sign).