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.
The Krakken - S1-E3
Continuity mistake: When The Krakken snatches the Cannery crate from the boat, you can see that the lower horizontal bar from the 'E' is suddenly missing, thus reading 'Cannfry'.
The Krakken - S1-E3
Continuity mistake: When Ben pretends to be sucked into the lake, and Gwen turns around to look after him saying "I'm not falling for it", she's missing her eyebrows for a second or two.
The Alliance - S1-E8
Continuity mistake: When Rojo attacks the police academy, there is a patrol car right behind her. But when Ben (as XLR8) arrives and slams into her, the car suddenly vanishes.
Continuity mistake: 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.
Continuity mistake: When the Tennyson's RV passes by Rapid City when it comes under attack by Vilgax, it's the first time the outskirts can be seen. But later, when the gas station explodes, the entire town is suddenly hidden behind a mountain range.
Continuity mistake: The number of rockets Sixsix has on his wrist launcher alternates between three and four, especially during the final combat scenes.
Continuity mistake: When the Marty-alien removes the dumpster as Ben watches him, there is a set of stairs leading down. But later, when Ben (as Wildmutt) and Gwen jump down the shaft, the stairs are gone and there is an iron ladder.
Continuity mistake: When Ben is upset because he is too short to go on the water slide, he is wearing a bathing suit. But in the shot where the Omnitrix deactivates and he is back to being a human, he is in his normal uniform.
Continuity mistake: When the three old people throw the car at Ben and Gwen, Ben doesn't have the Omnitrix on for a few seconds. (00:14:10)
Continuity mistake: When grandpa Max first wakes up in the fungi cave, we find him completely wrapped in tendrils. But when XLR8 comes to cut him loose, Max' shoulders are suddenly free.
Continuity mistake: When Ben, Gwen and Max try to track down Ghostfreak, Max's scanner picks up "trace spectral activity from around that corner", which happens to be right ahead, but then Ghostfreak and cohorts appear from behind. In a deleted scene featured on the series' DVD, the source of the reading is revealed to be the tuba player Ghostfreak had possessed, who instantly runs off at the sight of Fourarms.
Ben 10 vs. The Negative 10: Part 2 - S4-E9
Continuity mistake: 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.
Continuity mistake: Fourarms Gwen launches four bowling balls with all her arms at the same time, but the balls strike the pin sets one at a time.
Continuity mistake: The priest who presides over the wedding gets a faceful of muck by the bride's parents. When he flees the scene, screaming, he is peachy-clean, but later, as the ceremony is happily concluded, he suddenly has muck stains on his head and robe.
Continuity mistake: Season 4, episode 9 "Ben 10 vs. The Negative 10, Part 1": When Charmcaster taunts Gwen about not having "taken off the training wheels", she moves her head upward. Note that the lower part of her ponytail falling over her backside does not move as the upper part does, but remains fixed in place.
Continuity mistake: As grey matter is running to avoid being smashed by presents he isn't seen till he randomly appears on the second present. (00:17:45)
