Continuity mistake: When XXXX is awakened by Dragan's phone call, there is a gun lying on his pillow. In the overhead shot the gun is pointing in one direction; in subsequent shots it is pointing the other way.
Revealing mistake: When Gene's bodyguard (the one with the moustache) shoots Slasher and Duke, just before Slasher is shot the bullet hole effect is visible on her forehead (sightly concealed by make-up) just before the actual 'shot'.
Revealing mistake: When XXXX is in Greenwich Park with Mr. Lucky and he gets shot, Dragan shoots at the grass in front of XXXX. Grass is thrown into the air, and you can see white smoke coming from an explosive for the special effects.