Good Buu (Majin Buu) also known mainly as Majin Buu is the result of the Innocent Buu using fission to split into good and evil halves. He would go on to become a member of the Z Fighters and live with Mr. Satan. After the battle against the pure Majin Buu, Buu is referred to as Buu instead of Majin Buu and to the world he becomes Mr. Buu.
Good Buu is an entity of pure good and is very kind, caring, and playful.
Once he was absorbed by Evil Buu, his playful and childish traits manifest in Super Buu and Kid Buu respectively.
During his second battle against Gotenks, Gotenks was preparing the Super Ghosts of his Super Ghost Kamikaze Attack for battle.
Piccolo showed Gotenks that Buu had already regenerated from the last Super Ghost attack.
Super Buu was also lying on his stomach, drinking a soda (though it looked like a milkshake) and reading a magazine, much to Gotenks’ fury and embarrassment.Also, when Goku and Vegeta were preparing for battle, Kid Buu was sleeping (as Buu only needs a little time to rest), much to Goku’s surprise.
More importantly, due to his connection with Mr. Satan, he had the influence to stop him from killing the former as Super Buu and later Kid Buu.
For this reason, he also responded to Videl’s request to be patient due to being Mr. Satan’s daughter; though it wasn’t enough to stop him from killing her.
While mildly annoying to Super Buu, it infuriated Kid Buu enough that he spat him out as soon as he was able to.
Despite his good nature, it is shown in Dragon Ball Super that when he is hungry, Good Buu can be foul tempered and grumpy like when he interrupted Mr. Satan’s press conference and is also shown to be quite gluttonous as he selfishly refused to share one of his pudding cups with Beerus.
He also gets angry much like his original counterparts especially when loved ones are hurt or dead, such as Mr. Satan.
However, these negative traits could be attributed to his childlike personality.