Revealing mistake: When closing the portals that spawn enemies using silver, Ash will stand there during the in-game cut scene as the portal shuts and do nothing. If an enemy spawns in the portal just before or as it's closing, it will start attacking Ash during the cut scene, and Ash just stands there taking hits until you're able to control him again.
Character mistake: When Ash talks to someone, a small scene plays out, and he will suddenly be standing there with nothing in his hand. But the moment the scene ends, he suddenly will still be holding whatever weapon he had before talking, like the shovel.