Clamulet

The Clamulet is a magical item used in a late episode of the cartoon show.

Mainstream Smurfs Media
It was used as means of hypnotizing everyone besides the user, who then had complete control over their victims. The pirate captain, while in possession of the Clamulet, could give any commands to his crew or the Smurfs and they would obey, being placed in a trance by the Clamulet's power.