Gogeta

Gogeta is the result of Goku and Vegeta performing the Fusion Dance and a hero from Dragon Ball Z and GT.

Fusion Reborn
After Goku successfully defeated the first form of Janemba, he struggled to defeat the demon's second form, even with help from Vegeta. Seeing no other option, Goku proposed they try using fusion and though Vegeta didn't like the idea at first, he agreed. However he failed to do the technique exactly right with Goku, resulting in the two of them fusing into the short, weak, and obese Veku. He was, obviously, no match for Janemba and was forced to run from the demon's assault for thirty minutes, stumbling around and farting in defense. Just as Veku was cornered and about to be finished off by the demon, the fusion time ran out and Goku and Vegeta defused. After an hour, they attempted the fusion again, while Pikkon distracted Janemba and succeeded, fusing into the powerful Gogeta. Demonstrating his great strength, the fusion easily defeated Janemba and destroyed him with the Starbust Breaker attack. As the negative energy that gave birth to the demon dissipated, the ogre, Saike, was left behind. Upon making eye contact with Gogeta, the ogre ran off in fear of the mighty warrior, which made him chuckle, before he defused back into Goku and Vegeta.

Dragon Ball GT
After Goku couldn't beat Omega Shenron, despite being in Super Saiyan 4 form, Vegeta who just became a Super Saiyan 4 thanks to Bulma's machine suggested they try using fusion and Goku found it funny he was the one suggesting it. While Gohan, Goten, Trunks, and Majuub fought Omega Shenron to keep him busy, Goku and Vegeta performed the Fusion Dance, becoming Gogeta once again. Now in Super Saiyan 4 form, Gogeta was easily able to fight the united Shadow Dragon, even toying with Omega Shenron and eventually taunted him to the point that he used his Negative Karma Ball to try and destroy Earth. Gogeta combined the ball with some of his own positive energy as he kicked it away into the atmosphere, causing the entire ball to change into positive energy. It resulted in a nuke-sized explosion, which reversed all the negative effects the Shadow Dragons had caused to the Earth. Eventually Gogeta blasted Omega Shenron with his Big Bang Kamehameha, forcing him to revert back to Syn Shenron. But as he prepared to finish the Shadow Dragon off with another attack, the fusion time ran out early (it only had been 10 minutes or 15 at the most). This was because of the enormous amount of power the Super Saiyan 4 form used and Goku and Vegeta defused, though Goku was able to destroy Omega Shenron later on with his Universal Spirit Bomb.

Abilities
Gogeta is extremely powerful, since he is a fusion of the two most powerful Saiyans in existence. He has superhuman strength, speed, endurance, and durability and can manipulate energy in the form of blasts and flight. Gogeta can use a variety of special techniques, such as the Big Bang Attack, a powerful energy sphere he fires from his outstretched palm, and the Super Kamehameha, a powerful energy wave attack, which are Vegeta and Goku's signature attacks respectively. Gogeta can combine these techniques into his Big Bang Kamehameha, which he performs by putting both his hands in front of him at a 90 degree angle with his palms out. He generates a bluish, white energy sphere in front of him and fires a huge, shockwave-like blast of energy from the sphere. Gogeta has a more powerful variation on this attack called the 100x Big Bang Kamehameha which made its first appearance in Budokai 3. Another signature technique he uses is the Stardust Breaker (Soul Punisher), where Gogeta raises his hand above his head and forms a rainbow colored energy sphere. He then throws it into his opponent, disintegrating them, though the effect is somewhat delayed. Gogeta has also demonstrated the usage of Super Saiyan forms, like his fusees, namely the normal Super Saiyan and the Super Saiyan 4 form, depending on what form Vegeta and Goku are in when they fuse. In Super Saiyan form, Gogeta demonstrated incredible power and as a Super Saiyan 4, he is even more so, to the point where he could toy with Omega Shenron, who couldn't be beaten by two Super Saiyan 4s.

Super Kaioken
Gogeta can use the Kaioken as a power booster which can help him in times of need.

Ozaru
As a Saiyan Gogeta has the abilty to transform when the moon is full but he needs a tail.

Super Saiyan 1
Gogeta can transform into a Super Saiyan 1 and is considered the strongest being in the universe.

Super Saiyan 2
As shown in Dragon Ball Heroes Gogeta has the ability to transform into a Super Saiyan 2.

Super Saiyan 3
Gogeta as Super Saiyan 3 can be considered the strongest being on earth. Only rivaled by Vegito.

Super Saiyan God
Gogeta gains the ability the same time Goku & Vegeta gains it. Gogeta can almost fight on equal footing against Beerus.

Super Saiyan Beyond God
After the Super Saiyan God Form vanish Gogeta gains this form and uses this form regularly.

Super Saiyan God Super Saiyan
Gogeta gains the ability the same time Goku & Vegeta gains it. While in this form Gogeta fights on equal footing againts Beerus.

Golden Ozaru
Gogeta has the ability to transform into Golden Ozaru and later gained the ability to take it to the next step.

Super Saiyan 4
The last known transformation Gogeta Used against the Shadow Dragon Omega/Syn Shenron. Gogeta is realy powerful in this form.

Trivia

 * In Fusion Reborn, Gogeta didn't demonstrate any of the cockiness he had in GT and took out his opponent quickly. When he was a Super Saiyan 4, his personality seemed to be more akin to that of his Potara fusion counterpart, Vegito.


 * Gogeta as a Super Saiyan 4 is considered to be the most powerful character in the entire Dragon Ball series and is the strongest character in the video games, Budokai 3 and Infinite World.


 * Gogeta is the only fused Saiyan character that actually defeated one of his opponents.


 * In his normal form, his hair is apparently black as seen from Veku's appearance as well as in the video game, Buu's Fury, when he dies.


 * In some of video games, Gogeta's alternate costume as Super Saiyan 4 is that of an infamous picture of the Super Saiyan 5 form that was made as an April Fool's Day joke.