DBZK Episode 24
From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
Friends Reborn! Zarbon's Hideous Transformation! is the twenty fourth overall episode in the Dragon Ball Z Kai series. The original Japanese title is "Yomigaeru Nakama-tachi! Bisenshi Zābon Akuma no Henshin" (甦る仲間たち！美戦士ザーボン悪魔の変身). The episode first aired on September 20th, 2009. It's original American air date was June 28, 2010.
While Goku continues training on his way to Namek,King Kai tells him his fallen friends from the Saiyan threat are with him even Chiaotzu.Goku fills King Kai in on the situation on Namek.King Kai realizes Frieza is there and orders Goku to stay away from his evil might.However Piccolo assures Goku he'll train hard so when he's revived they will take Frieza down.After talking to his friends in Other World,Goku continues his training at 50x gravity.Meanwhile Krillin and Dende head to Guru's home for the remaining Dragon Ball.Vegeta senses Zarbon and confronts him to fight.At first Vegeta proves a match for zarbon then he transforms into his more repulsive but stronger form.He defeats Vegeta with ease who passes out from exhaustion.