Vegito is the result of a fusion between Goku and Vegita using Potara earrings. Goku and Vegita must each place a single Potara earring on opposite ears, which causes them to instantly fuse together. Vegito appears during the "Kid Buu Saga," when Goku and Vegita decide to use the Potara earrings after being overpowered by the evil character Buu. Vegito is able to take on Buu but later defuses back into Goku and Vegita after being absorbed into Buu's body.
Trunks and Goten first use the fusion dance technique to become Gotenks during the "Fusion Saga." Unlike fusion using the Potara earrings, the fusion dance only lasts for 30 minutes before defusing Goten and Trunks into their separate forms. Similar to Vegito, Gotenks is able to overpower Buu but later becomes absorbed into Buu's body. Gotenks also makes an appearance in "Dragon Ball GT," which is a sequel to "Dragon Ball Z."
The Namek fusion is first used by Piccolo to fuse with Nail during the "Freiza Saga." This fusion requires one participant to place his hand on another, who is then absorbed into the other. Unlike other fusions, the Namek fusion does not change the appearance of the participant who absorbed the other. Piccolo uses the fusion to become powerful enough to battle Freiza. Piccolo uses the Namek fusion again during the "Imperfect Cell Saga" to fuse with Kami so he can battle with Cell.
Unsuccessful fusions occur when the fusion dance technique is improperly executed. This is seen during the "Fusion Saga" when Goten and Trunks accidentally perform the dance wrong. Unsuccessful fusions result in its participants becoming a less-powerful and physically obese entity. Participants must wait for 30 minutes for the effects of the fusion to end before they can attempt another fusion dance.