In Dragon Ball Z: Battle of Gods, Majin Buu appears as the rotund, childlike pink being who resides peacefully on Earth. This version of Buu is the result of the original, chaotic Kid Buu absorbing the Grand Supreme Kai, an act that suppressed his pure evil nature and gave him a more innocent, playful personality. He is often referred to as Good Buu to distinguish him from his more dangerous forms.

In terms of background, by the time of Battle of Gods, Majin Buu has been living with the martial arts champion Mr. Satan for several years following the defeat of Kid Buu. He has become a domesticated, if still unpredictable, member of the community, even being given the name Mr. Buu. He has a particularly close bond with Mr. Satan, whom he sees as a best friend, and with Bee, Mr. Satan's pet dog.

His personality is defined by a stark contrast between childlike innocence and immense, volatile power. He is generally carefree, playful, and kind-hearted, often speaking in simple sentences and referring to himself in the third person. His foremost motivations revolve around simple pleasures, most notably an insatiable appetite for sweets and pudding. This gluttony and his lack of social awareness are key drivers of his role in the film's plot. Despite his good nature, he retains a short temper, especially when his desires are thwarted or when his friends are threatened, though his anger is usually less destructive than in his previous evil incarnations.

In the story of Battle of Gods, Majin Buu's role, while not central to the final battle, is crucial as a catalyst for the conflict. He attends Bulma's birthday party on a cruise ship, where the God of Destruction Beerus arrives. When Beerus, who is seeking a fight with the Super Saiyan God, asks Buu for some of his custard pudding, Buu selfishly refuses and consumes all of it himself. This petty act of denial deeply angers Beerus, as the god is also a gourmand who does not tolerate being refused. Buu is the first among the Z-Fighters to physically challenge Beerus, rushing at him in anger. Beerus effortlessly deflects Buu's punch with a light tap and sends him flying into a lake. Beerus then retrieves Buu, slamming his head into Gohan's, which knocks both of them out. After this swift defeat, Buu remains unconscious for most of the subsequent battle between Goku and Beerus.

His key relationships are central to his character. His friendship with Mr. Satan is the most significant, as the champion acts as a moral compass and caretaker for the powerful being. Mr. Satan has even forbidden Buu from getting too angry to prevent a rampage. In the film, his relationship with Beerus is defined by this singular confrontation over pudding, highlighting how Buu's trivial desires can have cosmic consequences.

Majin Buu shows little to no character development specifically within Battle of Gods, as his arc had largely concluded in Dragon Ball Z. He is presented as a static, established figure: a former world-ending threat who has been pacified into a quirky, gluttonous, but loyal companion to Mr. Satan. His presence serves to demonstrate Beerus's overwhelming power, as Buu, one of the strongest beings in the universe, is dispatched with comical ease.

Regarding his notable abilities, Majin Buu possesses a vast and unique power set derived from his magical, amorphous biology. His body is highly malleable, allowing him to stretch his limbs, reshape his form, and regenerate from virtually any physical injury, including being blown to pieces. In the film, he attempts to use his raw strength and durability against Beerus, but his most signature techniques include the Transfiguration Beam, which can turn living beings and objects into candy or other food, and the ability to fly and project powerful energy blasts. However, against a being of Beerus's caliber, none of these abilities prove effective. His childlike nature, while a sign of his goodness, also makes him easy to provoke and outmaneuver in a serious confrontation.