Super Saiyan 2

"This form has power that surpasses Super Saiyan in all ways. Gohan naturally transformed into this form through his anger at Cell's brutal actions, while Goku and Vegeta learned it through harsh training."

- Daizenshuu 7, Special Attack Dictionary Super Saiyan 2 (超サイヤ人 ツー) is the direct successor to the first Super Saiyan transformation. It is very similar to the original form in appearance, though the power output is greater, as is speed and strength. Gohan was the first person to attain the form while fighting against Cell in the Cell Games.

Overview
According to the Super Exciting Guide, this form gives twice the strength of regular Super Saiyan.

Usage in the anime
The form is used concurrently with its appearances in the manga, although perhaps due to carelessness from Toei Animation, the form is sometimes very hard to distinguish from regular Super Saiyan. The characteristic electricity in the aura is absent in some appearances, such as when Vegeta fights Kid Boo, and sometimes the hairstyle is completely incorrect, such as in some episodes of the fight between Goku and Majin Vegeta where Goku's hairstyle is that of his regular Super Saiyan form (with four to six bangs) instead of the unique hairstyle he attains while using this form (one long, thin bang in the middle and two smaller bangs on the sides).

Usage in GT
GT barely makes use of Super Saiyan 2. It only appears a handful of times throughout all 64 episodes: Goku uses it briefly against General Rild to fend off being metalized, and displays it again while ascending to Super Saiyan 3 during his second battle with Vegeta-Baby; Gohan and Vegeta arguably use it against Super Android #17; and Vegeta arguably uses it against Super Yi Xing Long (Omega Shenron) in his final showdown. The electricity is absent in each case except for the last, and even then it doesn't stay consistently.

In the first volume of the GT Perfect Files, it is stated that Goku would often skip over the form because it didn't provide a "rapid increase". Oddly enough, in this same entry, it mentions that the form includes sparks in the aura.