Super Saiyan 2 is the second level of the Super Saiyan transformation, and exceeds the previous form's power by a larger amount than the Ascended Super Saiyan transformations. [Ascended Super Saiyan and Ultra Super Saiyan are in this category, in which the user buffs up.] In addition, it also outweighs a Mastered Super Saiyan's power output.
With respect to the highest level of Super Saiyan 1 (unmastered or mastered), it multiplies the user's power level by 5 times their Super Saiyan transformation. This means that if the Super Saiyan 1 is unmastered, it's merely 250, but if it's mastered, it's by 1500.
In addition, this form can be mastered to increase the multiplier from 5 to 7. Goku and Vegeta have done this during the Buu Saga.