Goofs

When Phoebe and Paige visit Piper in the hospital, she has just finished a meal. However, as she was in labor, she would not have been given food or drink.

When evil Chris and Leo are up on top of the bridge, the background footage of San Francisco is clearly a still image instead of a video. The water is not moving and there is a boat stuck in the same place.

In the parallel world where everything is opposite, Barbas the demon of fear becomes the demon of hope. But the opposite of fear is courage, not hope.

When Gideon stops the potion vial, the glass cuts his hand badly enough that he leaves a trail of blood on the floor starting right next to the potion. Yet Leo and Chris don't seem to notice the blood. Although the blood may have disappeared when he and his counterpart healed each other, there was still plenty of time for Leon and Chris to notice it.

The suddenly introduced concept of an "opposite world" invalidates the entire premise of the whole series of the grand struggle of good versus evil. If no side can ever prevail for fear of throwing the cosmos out of balance then all that both sides ever do to gain superiority is of course utterly pointless.