During the end battle as Ash starts running over the deadites with his steam powered modified car one of the skeletons can be heard shouting, "It's the one in the car we want, get him!" but cars hadn't yet been invented at the time.
When Ash is fighting the hag after building his mechanical hand, he reloads his double-barreled shotgun and fires four rounds instead of two, and between each of these shots you can hear an audible re-cocking sound as you would from a pump-action shotgun. This sound would not be heard as there is no pump-action on a double-barreled shotgun.
During the Deadite siege, Ash dramatically orders the front gate barred. But the castle is equipped with both an outer and inner portcullis, which are specifically designed to frustrate would-be invaders. All the bar does is prevent their use.
During the first sword fight between Ash and Evil Ash, Ash's sword is the same length as Evil Ash's. Afterwards, when Evil Ash yells, "Back-stabber!" and pulls out Ash's sword from his body, the sword is small like a dagger.
After Ash shoots Arthur's sword, you can see something on the side of the broken sword that faces Arthur's surprised face. It could have been the device that blew the sword apart, or something attached to the back of the sword that had to do with it being broken for the shot.
When Ash is lifted out of the pit by the chain, he barely escapes having his legs crushed by the rapidly closing spiked walls by kicking the monster hanging on to them off in the nick of time. However, this same monster, which should have been crushed, emerges from the pit soon after.
When Ash straps Evil Ash to a table he revs his chainsaw. The chainsaw chain rotates in the wrong direction. All chainsaw chains travel in the direction that would pull the saw toward the tree when cutting with the underside of the bar (exiting on the top and returning in the bottom). It's a fundamental safety issue.
At the beginning of the movie Ash is being chain-ganged using a wooden stocks that bind his wrists and his neck, each through a separate hole. However, although his right hand had been self-amputated at the wrist, he seems unable to free his arm by simply pulling the stump out through the restraining cuff.
After Ash climbs out of the pit we see that the holster for his shotgun is empty. Then moments later Ash uses the shotgun to shoot Arthur's sword. But it's quite likely his rescuers retrieved the shotgun separately (and in the Director's Cut, you can see one of the locals handing it to him).
Some viewers believe they see Ash landing on mats when he falls through the portal,(which is too clearly seen to be a 'goof'), however on closer viewing they are, in fact, the *Large Paving stones* that led up to the cabin; There are 3 visible, yet Ash barely lands partly on only one. You can plainly see them because it's shown in slow-motion.
When Ash fights Evil Ash, his mechanical hand switches from his right to his left hand. Also in the same fight, it can be seen that Ash has both his hands at one point, even though his right hand should be the mechanical glove.
In the windmill, just before Ash steps on the nail, he suddenly has soot on his face. This is because of a deleted scene where he hits his head on the stove pipe, knocking it lose and pouring the soot in his face.
When Ash shoots Evil Ash in the face, Evil Ash jerks back before the shot fires and is actually in the air when the muzzle flash goes off. There is also a significant delay in the time between the click of the gun is heard and the blast.
At the end of the battle as Arthur's army advances towards Henry's army, one of Arthur's warriors carrying a seven foot axe passes in front of Ash. After Shelia becomes human again, while hugging Ash, the same warrior with the same seven foot axe passes in front of them again.