Continuity mistake: Near the end of the film, when Elsa and Clive are burning Dren's things, Elsa finds some drawings that Dren did of her. When she first pick up the pile, there are four drawings in her hands. When the camera pans out, instantly there are several more.
Other mistake: The DVD cover that has older Dren posing naked with her tail blade or stinger exposed shows her hands on the far right side crossing, and her hand has five fingers. In the movie her hands only have four fingers.