Continuity mistake: When Sam is looking for Darrin to tell him the good news, Aunt Clara walks into the living room holding the large book with its cloth bookmark hanging over the top front of the book (facing Sam), but in the next shot the bookmark has switched to hanging over the top back of the book (facing Clara).
Continuity mistake: When Aunt Clara tells Sam not to worry about Darrin because she has her book of spells, there's a closeup of the book with its binding facing left and Clara pointing to the large title "Spells and Incantations" on its cover, but in other shots Clara's holding the book with its binding facing right (we see Vol. 7 on the binding) so the cover is facing the opposite way, and there is no title on the cover.
Continuity mistake: Aunt Clara crashes into the pagoda and is helped up by Darrin and Samantha. They head inside and you can see Aunt Clara's purse sitting in the pagoda to the bottom left. But when all three enter the house, Aunt Clara is now carrying her purse.
Revealing mistake: When Samantha and Endora are in Paris reviewing models in dresses, the models are frozen because Samantha and Endora are not supposed to be in the dress shop. One of the models, instead of being frozen, is seen blinking her eye and moving slightly.