During the battle at the third castle, there is a sequence where Hidetora emerges from the castle at the top of a flight of stairs and confronts enemy soldiers ascending the stairs. When he retreats, his bodyguards suddenly appear and retreat with him, even though they were not present moments earlier.
During the first scene (while the Land Lord and his sons are hunting wild boars) the first shot that shows every single wild boar running in front of the camera is probably a single shot of the same wild boar repeated 3 times.
The goof items below may give away important plot points.
When Lady Kaede is decapitated by Kurogane, a big stain of blood from Kaede's head appears on the wall behind her. Then, when Jiro and the man are leaving the room to go to the war, the stain on the wall appears completely different.