Super Saiyan

Super Saiyan is a form assumed by extraordinarily powerful members of the Saiyan. It is used various times in the Dragon Ball GT series by many people, such as Goku, Vegeta, Gohan. It made its Dragon Ball GT debut in "Goku vs. Ledgic"

Search for the Black-Star Dragon Balls
The Super Saiyan form is used against various enemies, like General Mutchy Mutchy, General Rilldo, etc.

Battling Baby
The Super Saiyan form is used by Goten who fights Baby, which the latter eventually gets taken over by Baby. It is also used by Gohan and Baby-Goten who fight in the mountains. The form is used by Baby Gohan against Vegeta, who the latter also uses the form against. When Goku battles Baby-Vegeta, he uses the Super Saiyan form first, and then powers up to Super Saiyan 3, though this doesn't work as well. Goku eventually defeats Baby as a Super Saiyan 4.

Super 17, the Ultimate Android
The Super Saiyan form is first used in this saga when Goku and Vegeta are about to fight on the bridge, but Goku suggests that they get a bite to eat first. It is then used by Gohan, Vegeta, Goten, and Trunks to battle Super 17, though this proves futile. Goku uses Super Saiyan to combat Super 17, but the latter transforms to Super Saiyan 4 and defeats him later on.

The Strongest Shadow Dragon.
The Super Saiyan form is used by Gohan, Goten, and Trunks so Goku can borrow their Saiyan powers to push his physical self to it's limit, and when Gohan fights Syn Shenron.

Death of Omega Shenron
The Super Saiyan form is used again by Vegeta, Gohan, Goten, and Trunks, to combat Omega Shenron, though this proved futile, as Omega was much stronger than a Super Saiyan. Omega is then defeated by Goku's Universal Spirit Bomb.