Left Behind - S3-E10
Continuity mistake: In the previous episode Ra's al Ghul stabs Oliver through his chest, just below his left pec. When he pulls out the sword, a wound is visible. (However, seconds later, the wound is absent - different mistake). In this episode he is shown with a wound much lower (in his lower abdomen) and also later, with a bandage around his waist instead of his chest. (00:09:30 - 00:41:30)
Nightmare on Christmas - S3-E22
Continuity mistake: When Power Man is wearing White Tiger's tiara (her Christmas gift), he has it on point-side down. White Tiger grabs it with both hands and puts it on and it's now point-side up, without her flipping it. You also see it go from a partial band tiara to a fully enclosed band tiara, like a crown.