Factual error: The story is set in 1976. "Funkytown" is used in the movie and the end titles. The song was not released until 1980.
Other mistake: When dragon Belle Bottom holds him up to her face and says "and now you're gonna pay.", there's no reflection of the terrified Gru in her eyes.
Continuity mistake: In the final battle, Kevin (as a rabbit) runs up a wall and smashes his foot into tiger Svengeance's head. Svengeance's helmet is not on his head in this shot, but in the very next shot his helmet is back on.
Character mistake: Gru doesn't recognize Nefario at the record shop, despite meeting him at Villain Con in the Minions movie. And given the fact that he can recognize all of his Minions without even asking them who they are, he should definitely remember seeing Dr. Nefario.
