During the fight against Baby (whom has possessed Vegeta), we see Goku transform into a Golden Oozaru. The Supreme Kai, and Old Supreme Kai, pulled Goku's tail back out, so as to release his Saiyan power as fully as possible. When Goku looks up to Earth, it reflects enough light (17 million Zeno units to be precise) to transform him into an Oozaru. However, as Goku is now a much stronger warrior, his Oozaru transformation boosts up even more to become a Golden Oozaru, as opposed to a normal Oozaru. The power boost of a normal Oozaru is considered to be 10x, so you can imagine this Golden Oozaru transformation would increase the power even more!

Goku is unable to control himself in his Oozaru form, and so is unable to control himself in the Golden Oozaru form. When Baby Vegeta is exposed to enough light (using a series of rays created by Bulma), he too transforms into a Golden Oozaru. However, he is able to retain his reason and controls himself.

Super Saiyan 4

Goku is the first to transform into a Super Saiyan 4, and does so during the fight with Baby Vegeta. While in the form of a Golden Oozaru, Pan pleads to him to gain reason & control; Goku looks to the Earth, and remembers who he is, and who he's fighting for. And as soon as he touches Pan's tear-drop, he regains control of himself and transforms into a Super Saiyan 4. Goku becomes an adult again while in the SS4 form, and his physical appearance changes. He has red fur across his torso and arms, as well as having a change in the style of his hair. His eye's gain a red-outlining, and the pupils change to a yellow colour.

Vegeta too transforms into a Super Saiyan 4, but only with the help of Bulma. Despite Baby Vegeta being able to control his Golden Oozaru form, he didn't transform into a SS4 because Baby interfered with Vegeta's genetic makeup too much. However, when Bulma creates the Brute Ray, Vegeta is able to transform into a Super Saiyan 4 because Bebi's fiddling is no longer present.