Other mistake: Before the battle, the leader of the waterbenders says that he will have everyone extinguish as many sources of fire as possible. When the firebenders come up from the ground at the start of the battle, all of the torches lighting the city are lit.
Other mistake: When Matt Damon is in the dark alley pursuing the intermediary who will lead him to the General, it appears, at the first sight of his right leg thigh holster, that the holster is empty. However, several scenes later, when the camera is behind him, you can see the reflection of light off of the magazine, in the magazine well of the pistol.