The Mysterious Hero is the sixteenth episode of the Piccolo Jr. Saga and the one hundred thirty-eighth episode in the Dragon Ball series. The original Japanese title is "Nazo no Otoko・Shen" (謎の男·シェン). It first aired on December 14, 1988.
Goku does not know exactly how powerful Piccolo will be. Surprisingly, those of the Kame group, who have seen Piccolo do not recognize him. Piccolo offers to allow Krillin to withdraw, but Krillin refuses. Piccolo taunts Krillin with laughter and Krillin launches into a furious attack on Piccolo. Piccolo assures Krillin he won't kill him, only that pain is on the way. The wind picks up and dark clouds roll in as Piccolo charges his attack. Piccolo's arm extends and he plucks Krillin from across the stage and punches him toward the wall. He then throws Krillin in the air, and Krillin fires a Kamehameha. It hits an afterimage and Piccolo slams Krillin back to the ring. The clouds disperse, Krillin is still conscious though exhausted, as he can't even stand. Krillin forfeits the match, and Goku helps him out of the ring. Another childhood flashback ensues, Piccolo notes that he may have overestimated the ease of taking over the world.
Yamcha next prepares to fight the seemingly lucky nerd, Hero. Everyone assumes Yamcha will win, with no problems. Yajirobe watches the match, apparently the only one who thinks Hero will win. Goku sees that there is something stranger than everyone else thinks about Hero. Yamcha lets Hero attack first and Hero accidentally lands a kidney shot. Yamcha goes to kick Hero out of the ring, but Hero ducks and Yamcha lands on his back, slamming his crotch onto Hero's head.Yamcha is infinitely embarrassed, his pride is shot. Master Roshi sees that Hero is not being clumsy on accident. Hero tries to educate Yamcha, but Yamcha will not listen. Suddenly, Hero reveals he has extreme speed and skill, just as Roshi thought, and Yajirobe knew. Yamcha uses his Wolf Fang Fist, but Hero blocks it and kicks Yamcha's feet from under him. Hero continues to educate Yamcha in the ring.