In "Smurfette Unmade," when Scrupple said to Gargamel that he could not turn Smurfette back to her "evil" original self, his left hand shows four fingers. He should have five fingers in his hand.
In "Smurfette Unmade," Gargamel thought of turning Smurfette back to her original self was something he never though of previously. However, in "Smurf Colored Glasses" (from Season 1), he almost did change Smurfette to her original self until an unexpected visit by a hungry Bigmouth stopped him.
In "Smurfette Unmade," Smurfette threw eight vials of Gargamel's gold-making potion at him, Scrupple, and Azrael, even though there are three vials next to her.
In "Smurfette Unmade," none of the Smurfs ever realized that Smurfette was wearing a different dress and shoes, as well has a large nose typical of male Smurfs when she was changed to her original self.