Starring: Tara Strong, Dee Bradley Baker, Paul Eiding, Meagan Smith
Ben 10 vs. The Negative 10: Part 2 - S4-E9
Plot hole: 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 mistake: Season 4, episode 10 "Ben 10 vs. The Negative 10, Part 2": When the Forever King makes his announcement "Nothing will stop this little home-coming", he stands outside the Mount Rushmore base on bare soil. But in the scene where Max reviews the recording of this speech, all of a sudden we find the Forever King standing on a neatly tiled floor.
Grandpa Max Tennyson: Being a hero isn't about letting others know you did the right thing, it's about you knowing you did the right thing.
Ben Tennyson: What were you just doing, reading greeting cards back at the Mega Mart?
Grandpa Max Tennyson: Well... yes.
Back With a Vengeance - S2-E13
Trivia: About all of the aliens found in attendance of Kevin's mega cruiser strangely resemble those individuals previously seen (on the selfsame ship) in episode 2-5, "Grudge Match", whereas they should have escaped the cruiser near the end of that episode.