Character mistake: After Anakin says to use the walkers (AT-TEs) as boarding vessels, Rex calls the first one an AT-AT (a vehicle that does not even exist at this point in-universe) while ordering a battalion of clones into it. (00:04:10)
Burple Nurples/Shnitzel Makes a Deposit - S1-E2
Character mistake: In "Burple Nurples", Chowder was selling Burple Nurples for 5 dollops each. Later, Mung Daal steals a tray of six Burple Nurples, and Chowder runs after him, telling him that he owes him 300 dollops, instead of 30.
Suggested correction: The tray had more than 6, even if it was drawn to look like just 6, they could have been stacked on top of each other. Later when they're dumped in the fire, you can see more than 6 go in. Plus at that point we don't know how much Chowder was selling them for since it was after Mung Daal (while in disguise) paid more than 5 dollops for one.
Cat on a Hot Steel Beam - S1-E60
Character mistake: As the fire truck darts out from a back alley, the sign on a nearby gift shop window reads "gift's" when it should be "gifts".
Character mistake: When Rarity sees her cat stuck in the tree, Rainbow Dash is sitting next to the cat, but when you see her, her cutie mark is not there. (00:17:15)
Six Forgotten Warriors Chapter 4: The Six Fight Again - S5-E5
Character mistake: When the Red Skull reemerges from the vortex, he sees Chameleon and acknowledges him as his stepson. However, only moments before this, Kragov explicitly stated that the Chameleon was more like an adopted son to the Red Skull.
Character mistake: Season 3, Episode 2 "Squirmy". Little Bill and his brother, Bobby are returning his pet earthworm to the soil. Bill calls his brother by the name Jamal. Jamal is Little Bill's baby cousin.