King Kai taught Goku both Kaioken and the Spirit Bomb, which became his signature for a while. Kaioken is extensively explored in DBZ before Goku turns into Super Saiyan. After SSJ was introduced ...

Using the Kaio-Ken, Goku could have shut Vegeta down fast, and prevented him from awakening Majin Buu. The climax of the Buu Saga is brilliant, with the Spirit Bomb finally succeeding at defeating ...