Continuity mistake: When the Wicked Scary Monster first reveals itself in the Titan's Tower, we see the Titans huddled together in chibi-form after the commercial break. At first we see the Titans cowering behind Robin, who is standing in the middle, but when we see the Monster again up front, suddenly Starfire has taken the center and Robin stands between her and Beast Boy.
Continuity mistake: The animated video shelf which goes after Beast Boy uses red and grey DVD cases as eyes and teeth. When Beast Boy roars at it as a T-Rex, the shelf loses its "eyes" and "teeth" out of fright, but when Beast Boy charges into it, it suddenly has them all back on.
Continuity mistake: After the video rental clerk shoves the Wicked Scary DVD into Beast Boy's face, the scene fades to the evidence room where Robin is depositing Control Freak's remote. In the showcase to the left which holds the masks of Slade's robots, we also see some of the Puppet King's Titan puppets and his soul-switching control, which got crisped in blue fire in first season's "Switch"; therefore it should not be on display. (Switch to slow run to detect it; it's rather difficult to catch on normal speed.).
Continuity mistake: After claiming to Cyborg (her last remaining teammate) that she never gets scared, Raven turns away to find him missing; at that point you can see the cellar door in the right-hand wall. But when the winged shadow monster appears and Raven turns to run, the cellar door is gone.