Super Saiyan God (超サイヤ人ゴッド) is a Super Saiyan transformation that surpasses Super Saiyan 3. It appears in Dragon Ball Z: Battle of Gods and a couple of video games, and represents the other 'God' in the Japanese title for the film: Dragon Ball Z: God and God (ドラゴンボールZ 神と神), as well as the reason for the plural "Gods" in the English title.
When in this form, the Saiyan's general appearance remains unchanged with the exception of a few slight differences: the skin tone becomes darker; the hair lifts up slightly and adopts a reddish-purple coloring; the Saiyan's eyes grow, becoming sharper and the irises become red; the overall body structure appears to become thinner and slightly taller; the aura becomes more explosive and flame-like in appearance.
Usage and power
The power of this form is great enough to allow Goku to fight on par with the God of Destruction Beerus, who had effortlessly defeated Super Saiyan 3 Goku, Ultimate Gohan, Majin Buu, Super Saiyan Gotenks, and a fully powered Super Saiyan 2 Vegeta. As such, it is currently among the most powerful Super Saiyan transformations in all of Dragon Ball Z. In fact, it is so powerful that none of the Z Fighters can sense Goku's energy while he is in this form, the form even makes its user completely immune to Demigra's Dark Magic. This form also allows the user to sense godly ki, and they can absorb attacks by consuming ki. In addition, Goku as a Super Saiyan God is given a signature attack called 'Kamehameha Rebirth' in a few of the video games. As powerful as it is, however, it also has drawbacks: the form drains the user's energy reserves fairly quickly, thus creating a time limit, although it is speculated by Beerus that this limitation could be overcome.
Unlike the other Super Saiyan forms, Super Saiyan God is not a permanent transformation as far as we know so far. In Goku's case, during the events of the film, he is seen losing the form, yet retaining the power, allowing him to continue to battle Beerus on equal grounds in his base and Super Saiyan forms.