Visible crew/equipment: When Blankman and his brother escape from the bank just before it explodes they are diving on the ground to escape the explosion. You can see that Blankman's brother is a stunt double. (01:04:30)
Revealing mistake: When Blankman is using his homemade grappling hook, you can see that the string is attached to the top of the invention and turning the handle isn't doing anything as he's simply being lowered.
Continuity mistake: After the Grandmother dies and Blankman is walking home with his brother, we see a car pass with a wheel lock on the front driver's side tire. When we see it again a few shots later, it's now on the passenger tire.