Continuity: Season 4, episode 9 "Ben 10 vs. The Negative 10, Part 1": When Charmcaster waves her good-bye to Gwen just before Animo swoops her up, the coloration of her waving sleeve's decor suddenly changes from violet to purple.

Revealing: Season 4, episode 5 "Ben 4 Good Buddy": When the Baron drives off from the garage in the Rust Bucket, the VR's interior shifts unnaturally; an obvious glitch in the computer animation.

Plot hole: 4-9 "Ben 10 vs. the Negative 10 (Part 1)": Rojo (from first season's "The Alliance") makes her second appearance in the series in a suit of powered armor. However, in "The Alliance" she had been turned into a cyborg by Vilgax' drone and thus looked radically different than she does here. So how can Max say: "How did she get back her alien tech?" when her equipment and weaponry was totally different in their first encounter?

Continuity: Season 4, episode 10 "Ben 10 vs. The Negative 10, Part 2": As we could see in first season's final episode, "Secrets", Roosevelt's head on Mt. Rushmore was totally destroyed, and in most subsequent episodes - including this one's first part - there is a sizable hole in its place. But after Ben asks whether the plumbers' hologram technology can replicate 'big presidents', and the scene changes to the demolished presidents' heads, the crown of Roosevelt's head suddenly joins the others on the mountainside.