Revealing mistake: Ash faces the oval, wall-mounted mirror and tries to reassure himself that he's fine, until his mirror-image lunges out and tries to strangle him. Throughout this scene, the background set and lighting "reflected" in the mirror changes very noticeably between the real mirror and the hole-in-the-wall practical effect. Additionally, the Ash that lunges through the mirror is NOT a "mirror-image" of the other Ash, as the blood patterns on their faces are distinctly different, which is obvious in the face-to-face profile shot. For that matter, the blood patterns on Ash's face are inconsistent all throughout the film, frequently from one shot to the next.Charles Austin Miller
Revealing mistake: When Evil Ed tears off some of Bobby Jo's hair and eats it, the head is made out of latex (Watch for how easily everything bends on his face, even the jawbone bends at one point).