The Kamehameha Wave - S1.E8

Once they land on Roshi's island, Goku and Chi-Chi explain to him their dilemma--Chi-Chi and the Ox King can't get into their castle until the flames on Fire Mountain are extinguished. Roshi agrees to give them the Bansho fan if Goku can convince Bulma to get him a date with an older woman. Unfortunately he realizes that he used the fan as a place mat, then threw it away when it became sticky. He then accompanies them to Fire Mountain to extinguish the flame himself with his Kamehameha Wave. He succeeds, but he accidentally destroys the castle and the mountain too.