Dragon Ball Z - episode 18 - 05 Sep, 1989

Gohan continues his martial arts training under the watchful eye of Piccolo, but a strange transformation takes him over. A full moon causes the young Saiyan to rampage out of control! Meanwhile Goku finally makes it to the end of Snake Way and mistakes a friendly ape named Bubbles for the mythical King Kai. With two of our heroes going bananas it looks like the two sinister Saiyans will have an easy time invading Earth! (Source: dbzepisode.org)