Revealing mistake: When Marty and Shamus are sharing a meal at the dinner table, Shamus passes Marty the plate of rabbit. As Shamus hand moves away to let go of the plate, to the bottom right hand corner of the plate, a purple patch appears briefly where the two M. J. Fox actors interact, an error with the Vistaglide camera tech used back then. Easier to spot on Blu Ray Version, better than DVD.
Revealing mistake: At the very end of this film, Doc appears in his locomotive time machine. In every shot the plate which says 'ELB' changes color. From red to orange. You would say this is a change in light angle, but when the locomotive rises and turns, you can see every angle of this plate and in every angle this plate is red.