Continuity mistake: When the matchmaker grabs Mulan's hand her palm is shown to be covered in ink. She then unwittingly paints herself a goatee. However, immediately after this she grabs the teapot's handle but no ink rubs off onto it. The ink miraculously disappears from her palm as well.
Deliberate mistake: During the movie, when Mulan is just a girl, you can see that her eyelashes extend beyond her eyes. When she is pretending to be a boy, her eyelashes are short (this makes perfect sense). But when she is in the medical tent her eyelashes are long even though she had no time to put on makeup. This is deliberate though, because without it she would have still looked like a boy, and just pulling her hair down wouldn't make her look any different (since that's how she looked in the pond). So they had to change her eyelashes to make her look more girlish.
Continuity mistake: In the final battle scene, Mulan has her ribbon around the wire to begin sliding down, but then decides against it. The next shot of her running toward a fallen knight, there is no ribbon visible. Also, the giant sword mark that was left after she cut down the wire has vanished.
Continuity mistake: The wagon, which is full of explosives, is on fire, so Mulan cuts Kahn (the horse) free with her sword and jumps onto Khan. She starts to ride away, while she holds the reins in her left hand and the sword with her right hand, up in the air. The wagon explodes and in the next shot, she still holds the reins in her left hand, though the sword, still in midair in her right hand, is now actually in its sheath, which is always attached to the left side of her belt. Some arrows are missing on the ground as well.
Continuity mistake: When the soldiers arrive at the city that has been destroyed by the Huns, there are no footprints except for those of the soldiers. But there should be thousands of them left from the Huns ,army, and villagers who battled there. (And this was not because it snowed and covered the prints up. If it had snowed the buildings would be white.)