There are four ways to achieve this transformation, a requirement for all four is that the
Saiyan must first gain a large quantity of energy (usually by training), far beyond that required for the first Super Saiyan form. The first method is that the Saiyan must experience a powerful emotional upheaval, much like the Super Saiyan transformation, but to a greater extent. Because of the intense emotion required to initiate the transformation, any
mastery of the Super Saiyan state and mental stability attained therein is negated, and the naturally remorseless nature of the Saiyan race is magnified, requiring them to master the personality adaptations to an even higher degree. Even Gohan with a gentle and docile personality became a hotheaded, merciless fighter after transforming, opting to torture Cell rather than kill him, despite
Goku's pleas. The second method to obtaining the transformation is simply through harsh training.
[8] The third method is merely through instinct from a desperate need; if the Saiyan is in a situation that needs a quick and desperate action, like saving somebody from almost getting killed, the Saiyan will instinctively and in a rapid instant, transform, quickly making them more powerful.
[9] The fourth method is for the Saiyan to feel out the tingly feeling in their back. The power output emitted by this form is greatly increased as well, as it doubles the strength of the regular Super Saiyan transformation.
[10][11]
Super Saiyan 2