Continuity mistake: When the cat was chasing Clumsy at the bench, Clumsy fell at the Anjelou box, and then Patrick suddenly covered the box with another box making Clumsy's box under that box. But at Patrick's apartment, Clumsy's box was at the top since he was peeking from it without any box at the top.
Continuity mistake: At the beginning where the Smurfs are rehearsing for the Blue Moon Festival, the Smurfs are dancing with the pond both left and right of them. But when Brainy ruins the dance, some dancers fall into the pond. Then when Narrator Smurf speaks, it's back to normal.
Continuity mistake: In the scene where Sofia Vergara takes Gargamel to lunch, Gargamel's cat Azriel knocks down a plate of bread. In the next shot, the plate is back on the table.