Continuity mistake: In the scene after the French General attempts to burn down the forest, Jacob throws the magical axe at the King's servant, who is attempting to kill him. The magical axe comes back and kills the servant. In the next scene, you see Jacob climbing the Tower, and on the ground you can see the axe, with no blood on it, and the body is nowhere to be seen.
Continuity mistake: When Wilhelm and Jacob arrive into the town, they get out of the carriage and start stretching. When Wilhelm is calling "Hello, good people, is anyone there?" Jacob is stretching, with one arm in the air and one by his side. It then cuts to a shot of Jacob through a window, and he has both arms in the air, with no time to change between shots.
Sasha: It's all right! They're the brothers Grimm! People talk about them in Marsburg! They're famous!
Will: Right you are son! The famous brothers Grimm. Look at this strapping young man.
Gregor: "He" is my daughter.
Will: And a fine wife he'll make some lucky man.