Continuity mistake: At the end when the 3 vampires are shooting at Michael, Selene drops behind them. The blood on the left side of her head disappears and reappears a couple of times. When she's taken them out it's back again. And it gets bigger and smaller all during the time it's there.
Continuity mistake: In the first scene when Rigel is crouching, taking pictures of the werewolves, he is holding the camera in his right hand just as he is about to jump down. However, when he is jumping, the camera angle changes and it can be seen that he is no longer holding a camera in his right hand.
Continuity mistake: When Lucian goes flying over Selene's car, in the overhead shot we see that the road below him has large parts with visible concrete because there are no paving stones. But in the next shot, a close-up of Lucian landing on his feet, the road is fully paved with paving stones.
Continuity mistake: At the shooting range, Selene is shown firing a black USP without a compensator. It then cuts to an over the shoulder shot, and she is now firing a two-tone USP Match (which she supposedly receives from Kahn to test out a few seconds later). It then cuts to a frontal shot of her, and she is once again using the same black USP. She never stopped firing, so she couldn't have switched guns.