Super Saiyan 2 (超サイヤ人ツー, Sūpā Saiya-jin Tsū) is the direct successor to the previous Super Saiyan transformation. It is very similar to the original form in appearance and attainment, however the power output is far greater, as speed, strength, and energy output all drastically increase. Gohan was the first person to attain the form while training in the Hyperbolic Time Chamber with Goku. However, because of the sheer power of this form, it lasts only a few seconds. He later completely achieved it in the Cell Games, after witnessing Android 16's tragic death.
in order to achieve this transformation, the Saiyan must first gain a huge amount of energy (usually by training), far beyond that required for the first Super Saiyan form. Once enough energy is acquired, the Saiyan must experience a powerful emotional upheaval, much like the Super Saiyan transformation, but to a greater extent. A Saiyan can also achieve Super Saiyan 2 level when intensly trained, much like Vegeta. Because of the intense emotion required to initiate the transformation, any mastery of the Full-Power Super Saiyan state, and mental stability attained therein, is negated, and the naturally remorseless nature of the Saiyan race is magnified, requiring them to remaster the personality changes. Even the gentle, polite Gohan became a hotheaded, merciless fighter after transforming, opting to torture Cell rather than kill him, despite Goku's pleas. The power output emitted by this form is greatly increased as well, as it doubles the strength of the regular Super Saiyan transformation, as stated by the Super Perfect Guide.
The golden hair brought on by the original transformation becomes longer and rigid; most of the hair that hung loose in the Super Saiyan transformation (in the case of Goku or Gohan, because Vegeta lacks any bangs in front of his face, as does Gotenks) is now raised. Increased energy radiation causes the aura to take on a jagged, fierce flame-like appearance rather than smooth or flowing. Because the energy output and radiation is higher than that of any Super Saiyan, the aura pulses at a higher frequency, like the type 2 aura, at least in the manga. Muscle mass is barely increased, but energy output is multiplied manyfold; such that greater amounts of the Saiyan's increased energy capacity can be used at once for much more powerful energy attacks without losing too much energy and feeling exhausted later, and even speed is augmented incredibly by the boost, unlike the Ascended and Ultra Super Saiyan states which cause the muscle mass to swell and thus impede the user. Another notable feature of the form featured in almost all Dragon Ball Z games and some scenes of the show as well as pictures from the manga, is the electrical aura, many electrical sparks (normally blue, gold in Dragon Ball Z: Budokai 3) that constantly surround the body — especially when charging up. However, they aren't always present (especially in the anime; Gohan and Vegeta aren't the only ones who lack the trait completely in some episodes), and some fans sometimes mistake a charging Super Saiyan for a Super Saiyan 2 due to the lightning sparks, such as for Vegito (in the manga, they never reappear in his aura after his final transformation, nor are they ever shown on any other first-level Super Saiyan).
According to Goku's flashback, Gohan technically first transformed into this form during their training in the Hyperbolic Time Chamber, though he was too exhausted to mantain it. This is the reason why Goku knew about this power before Gohan transformed into it during his fight with Cell. The first time the Super Saiyan 2 form was fully achieved and maintained by Gohan occurred after he witnessed the Cell Juniors' attack on the Z fighters and Android 16's death at the hands of Perfect Cell.The power of the Super Saiyan 2 form skyrockets far beyond the power of the Super Saiyan, Ascended Super Saiyan, Ultra Super Saiyan, and even Full-Power Super Saiyan forms. Perfect Cell and Bojack, who could both easily dominate those in the Ascended and Ultra Super Saiyan forms and were somewhat stronger than Full-Powered Super Saiyans even without accessing their full strength, were easily slaughtered by Gohan in his Super Saiyan 2 form. In addition, when Perfect Cell produced seven Cell Jrs., each of the Z Fighters were unable to fight evenly with even one of them (including Goku, Vegeta and Future Trunks, but the former was exhausted from his previous fight with Perfect Cell himself). However, when Gohan fought the Cell Juniors in his Super Saiyan 2 form, he killed all of them effortlessly on his own in simple, single blows, and was unaffected by their most powerful attacks.
Gohan proceeded to fight and severely injure Perfect Cell with just two punches, even after the android unleashed his full power. However, in a Kamehameha struggle against Super Perfect Cell, Gohan had a very hard time due to having his left arm broken by Super Perfect Cell's attack when he defended Vegeta after he attacked the Android to try to avenge his son's death (a blast which was stated to reduce Gohan's power output to less than half its normal amount). It was only a little help from Goku and Vegeta that Gohan needed to summon enough power to destroy Super Perfect Cell.Seven years after the Cell Games, Gohan demonstrated the Super Saiyan 2 transformation to Kibito at the World Martial Arts Tournaments and, according to the Daizenshuu, reused the form to fight against Dabura. However, Vegeta mentioned that Gohan's Super Saiyan 2 form was now much weaker than when he fought Perfect Cell due to his lack of training.
Following the events leading up to Majin Buu's revival, Goku and Vegeta (after becoming a Majin by Babidi's spell) fought evenly matched in their Super Saiyan 2 forms. The power of Majin Buu is shown to far surpass the power of the Super Saiyan 2 form; Vegeta inflicted little damage to the monster, and even after he expelled all of his energy at once in a devastating suicidal explosion, Majin Buu managed to fully regenerate after some time.When Vegeta returned to Earth from Other World (with the help of Fortuneteller Baba), he and Goku fought Super Buu in their Super Saiyan 2 forms. However, due to the massive power he achieved from absorbing Gotenks, Piccolo, and Gohan, Super Buu's strength easily outclassed Goku and Vegeta, reverting them back to their normal states. It wasn't until Goku finally convinced Vegeta for both of them to wear the Potara Earrings so they could fuse into Vegito, giving them enough strength to easily dominate Super Buu.
During the fight with Kid Buu on the Sacred Kai Planet, Goku and Vegeta battled while using the Super Saiyan 2 form for a short time, albeit in the anime only, as Goku went straight to Super Saiyan 3 in the manga, stating that he would have no chance if he did not use his full strength.It is stated in Daizenshuu #7 that Gotenks can theoretically transform into Super Saiyan 2. However, due to bypassing Super Saiyan 2 when transforming from a Super Saiyan into Super Saiyan 3, his complete Super Saiyan 2 form is never fully revealed, and remains unused.
Furthermore, during Dragon Ball GT, Gohan and Vegeta used the Super Saiyan 2 form from time to time during battle. However, by this time, it had been majorly outclassed by Super Saiyan 3 and the new Super Saiyan level, Super Saiyan 4. One strong case for Gohan and Vegeta's usage of the Super Saiyan 2 state is when they, along with Goten, Trunks, and Majuub, power up to fight Super 17. Here, the robust aura associated with the Super Saiyan 2 state appears on Gohan and Vegeta, but not on Goten or Trunks, both of whom never assumed the state; the lightning sparks, however, are not present. When Goku appears on the battle field, he fights Super 17 in the first level Super Saiyan state before using the Super Saiyan 4 form without any usage of either the Super Saiyan 2 or Super Saiyan 3 levels.
The Super Saiyan 2 form made its first movie appearance in the film Dragon Ball Z: Bojack Unbound, where the Z Fighters were struggling to combat Bojack and his henchmen. After being saved from Bojack by Goku (who used Instant Transmission to teleport to Earth) and hearing his father's words of encouragement, Gohan tapped into his Super Saiyan 2 powers and defeated Bojack and his henchmen in a matter of minutes.Gohan also used this form to battle Broly when the latter reappeared in Dragon Ball Z: Broly - Second Coming, and despite putting up a far better fight than he did previously, he was outstripped by the Legendary Super Saiyan's massive power. However, this was partially because of Gohan's lack of training that made him noticeably weaker up to that point, and since Broly survived being impaled in the stomach by Goku's punch in Dragon Ball Z: Broly - The Legendary Super Saiyan, Broly's power most likely increased substantially after recovering from near-death, as all beings with Saiyan genetics undergo when in the same predictament. Though, to Gohan's credit, his strikes managed to inflict a noticeable level of injury to Broly (whereas nobody in Broly's first appearance could damage him in the least), as Broly was knocked back when he was kneed in the face by Super Saiyan 2 Gohan.
The Super Saiyan 2 form was also used in the movies, Dragon Ball Z: Fusion Reborn and Dragon Ball: Wrath of the Dragon, against Janemba and Hirudegarn respectively. However, in both of the movies, either fusion or the Super Saiyan 3 form was used to kill the main enemy.