The New Fred and Barney Show (1979)

S1E7 Barney's Chickens

A magician casts a spell on Fred, convincing him that he’s a colossal chicken. In a twist of fate, Barney unintentionally mimics the magician's technique on Fred and a few others. Eventually, Barney comes to the realization that his only course of action is to hunt down the magician and request his help to reverse the bizarre situation.