Plot hole: Bonnie is the anchor for the other side and feels when supernatural beings die. How come she didn't know Katherine wasn't dead? Did she never think it was suspicious that she never felt Katherine's body after she died?
Revealing mistake: When Dylan and Tyr head to a bridge where supposedly the power source is located as well as Rommie, they start to cross the bridge. As the camera is facing Dylan and Tyr, the next scene two aliens teleport in. Rewind the video to facing Dylan and Tyr and play in slow motion. Watch the bottom portion of the screen and notice the top portion of one of the alien's head go into the camera as if the aliens walked into position for the teleportation.
Continuity mistake: In Episode 5, "Live Hard, Die Young and Leave A Good Looking Corpse": As Lillie is preparing to cut Zane's throat with her fingernail, she stands with her hand raised above her head for a while. When seen from the front, her hand is balled into a fist with the index finger extended, but when seen from the back all her fingers are extended. The view alternates like this several times, and each time the hand varies between fist and outstretched fingers.
Revealing mistake: When Rachel and Adam first meet, their cars crash in the car park. In the shot where they both get out of their cars, you can see a dry patch of ground under Rachel's car, but the rest of the area is wet. Why would that space be dry, if Rachel just crashed and it isn't raining heavily at the time?
Continuity mistake: Prior to the dinner at Fancy's with George's parents they show the restaurant from outside but the person in the window is the Veterinarian that Zoe stands up later this season and it is actually the same exact shot from when he is waiting for her to show up for their date.
Continuity mistake: While Josh and Cooper are fighting Gabi shouts, "You need to stop fighting.., because you're bad at it and it's embarrassing," then in the next shot the top shelf of the shelving unit is collapsed with nothing on it, but two shots later that shelf is fine with the books, plant, etc, all set up properly. (00:02:45)
Continuity mistake: Guy of Gisbourne says to Robin Hood that he should lay down his weapons. Robin Hood throws his bow and sword on to the ground. He then gets thrown down the cliff, into the river. A few minutes later, when we get focused on him again, we see that the bow is lying in the river with him. (00:06:05 - 00:10:55)