During Johnny Madrid's escape from the hangman, the gun Reece throws him fires off a miraculous 12 rounds without reloading.
Shortly after Danny Trejo's resident bartender character changes into a vampire, he's soon replaced by another taller, and obviously skinnier actor in vampire makeup, wearing the same clothes, and Danny is never seen again.
When Johnny and Esmeralda are riding to entrance of abandoned inn, the lights (electrical) of some city far at a horizon are clearly visible.
Several of the monstrous vampires are obviously wearing poorly applied masks, as the eyes are loose and not not properly glued to to the actor's faces.
At one point in the brothel area, one of the prostitutes is seen running away, you can see a white thong on her. Those were most likely not invented at that point in history.