When Hook (Killian) returns to the Sorcerer's house after Liam moves on, Hook is not wearing his earring (black stud), but then he is wearing it, then not again, etc. for the duration of the scene.
When, at the beginning of the episode, Henry (riding with Cruella in her car) sees a light in the forest, it is on the right side of the car. As he tracks the light, you see the car in the background on the road. They are in the forest to the left of the car. And the car didn't make a 180 degrees stop, as is clear when you see the car stop. So he is on the wrong side of the road.
When talking with the Apprentice, Henry mispronounces Cruella's name as "Carella".
Regina says she tore out pages from the story book so Henry wouldn't realize she was the Evil Queen. However, in Season 1 it is Henry who tore out pages from the book so Regina wouldn't realize that Emma was The Savior.