A Gummi By Any Other Name - S1-E9
Plot hole: The Changing Hat has the habit of transforming its wearer at the mere mention of a name (or even a species type, as seen before when Sunni accidentally transforms into an ogre). However, when Calla impersonates Igthorn and faces off against him, she loudly says the name "Toadwart" and doesn't transform.
The Beacon - S1-E26
Plot hole: Barrows introduces himself as "Dr. Dennis Barrows," and Teddy asks, "What's a doctor?" As the isolated villagers have never heard of doctors, Teddy would have no way to know that "Doctor" was a title/profession and not simply part of Barrows' name. He should have asked, "What kind of a name is Doctor?"