Continuity mistake: Scott becomes more monstrous due to his new Alpha status. He even says that he now has extra fangs but later in the series, these fangs are gone with no real explanation to what happened to them.
Other mistake: When we see young Peter Hale convince young Derek to turn Paige with Ennis' help, it is said that Derek is 15 when he killed Paige. And according to Wikipedia Derek was 16 and in school during the Hale house fire. Although when Derek is 15 we see Peter Hale played by a younger actor but during the Hale house fire Peter is played by Ian Bohen. How did Peter change so much in a year? Ian looks much older than the actor who plays 15 year old Derek than the actor who plays young Peter does.
Continuity mistake: The McCall house has its electricity shut off but at the end of the episode Scott's bedside lamp still works.
Perishable - S4-E9
Factual error: Lydia tells Stiles that as a child she was so obsessed with the book "The Little Mermaid" and insisted on being called Ariel for months. The thing is that the character wasn't named in the book, she was only given the name Ariel in the Disney film.
