In the last scene when she fights with the werewolf, countess rises from her coffin and stands in it, but in the very next shot it is closed and she is standing behind it.
When vampire Erika is seducing Waldemar, the mirror above them is supposed to show no reflection. When he lifts his arms, they are not reflected at all, but the same arms. The mirror is a projection of the same scene taken without Erika in the shot.
When the werewolf jumps out of the window, it's very obviously a fake window.
There two scenes at the castle, one when the thieves arrive and one when the girls arrive, where an obviously fake fog is shown. In fact, the second time is during the day and it's clear a fog machine is producing it.
A man shoots a crossbow three times in rapid succession. This would be impossible because reloading only one arrow would take a lot of time.
There is a scene where woman chokes a man to death, but he is choked to soon, while in reality choking someone takes a lot of time.
A woman knocks out a man by hitting him with a walking stick, but she doesn't hit him in the head and instead hits him more on the shoulder. Such a hit wouldn't knock you out.
Three times during the movie light sources are obviously reflected in the camera. First time it's the lantern the thieves are carrying and second and third time it's the candlestick.