Other mistake: During the first round of the duels we see a part of the participants list and "Scars" is missing. He should appear between "Spotted Horse" and "Sparks" according to their order of entering the competition.
Other mistake: When Leonardo DiCaprio is shot by Gene Hackman, he lays on the ground with his feet splayed out. The bottoms of his shoes are perfectly clean, no dirt, no dust, no wear and tear. The girl that is tending to him seems to have a french manicure, or very shiny perfect nails.
Other mistake: After Herod shoots Ellen Doc Wallace examines her and says she is dead. Obviously he is in league with Ellen and Cort, using the red ink to make her look dead. But earlier he says that Spotted Horse is dead, having "examined" him from several feet away. He is wrong, because Spotted Horse gets up and fires several shots at Cort. He would have no reason to fake that death, and is apparently a qualified doctor.
Other mistake: Final showdown between Ellen and Herod. The first shot hits him in the torso. He does not move and seems surprised to find a hole there. Second shot to the head, from the same gun, lifts him off his feet and drives him back several feet, a very different reaction. Quite possibly at some point it was supposed to be Cort that shoots him first, from behind Ellen. Ellen would be wounded but then fire the killing shot.