Kid Buu is the final villain of the Dragon Ball manga, and the second to last villain of the Dragon Ball Z series. Unlike his other forms, this form of Buu's thought process is seen to be irrational and spontaneous, even destroying his own body to destroy the Earth. Although he appears smaller than any other form, he is more dangerous than any other forms of Buu due to his full relentless evil and unpredictability. He is also completely free of restraint and has no trace of sanity and, because of this, is extremely volatile. He retains his childish personality, becoming amused and laughing hysterically at his own destruction of entire worlds.
After his death, Kid Buu reincarnated into Uub (ウーブ), with Kid Buu hidden inside his being.
Kid Buu is almost identical in terms of appearance to that of Super Buu, with the exception that he is childlike in terms of stature and his antenna also becomes quite short. In the manga, Kid Buu does not have any fingers besides the small index finger, but in the anime and video-games, he has the regular four fingers and a thumb. Just like the other Buus, he wears baggy white pants with a black belt showing the Majin symbol. Like Super Buu, he wears black arm covers.
Kid Buu's personality is very similar to that of a very young spoiled, selfish child, in that he retains no form of compassion or remorse for any of his actions. Furthermore, due to his selfish and capricious personality and mind-set, he is incapable of developing empathy and comprehending the nature of his actions. Kid Buu is also, like a child, very unpredictable in his behavior and actions, sometimes randomly falling asleep during battle, or acting like a monkey by banging his chest with his fists.
Buu's only reason for existence was to cause absolute destruction. He enjoyed the destruction he brought to the universe, reveling in the devastation he wreaks. He appears to enjoy testing the limits of his own power as well, seeking out Vegeta and Goku just to see how far they could push him. He is also utterly merciless, annihilating entire planets simply because Vegeta and Goku were not there. On the rare occasion he ever showed any restraint of his power, it was to make his "game" of destruction last longer instead of producing an instant kill. He is not a sadistic killer seeking to bring pain to his victims, as he seemingly does not care, or even know about pain, nor does he seek to conquer and rule over anything. He merely seeks to have fun the only way he knows how; creating havoc and destruction in the whole universe, similar to the fat version of Buu before Mr. Satan told him to stop killing.
Though he is highly irrational and insane, Kid Buu does seem to have some reasoning abilities and intelligence, as he quickly realized that Goku refused to hit him with the Spirit Bomb as long as Vegeta was in the way and took advantage of it by pinning the latter to the ground.
From all the forms of Buu, Kid Buu appears to be the least capable of speech. In the manga, his only phrase is "You've had it!" during the battle against Goku and Vegeta, his other words being mostly gibberish. In the FUNimation dub of the anime, Kid Buu's speech capacity is somewhat increased, as he says things such as "Buu squash you like bugs!", "Dum Dums!", "Me Buu, kill you!" and "Me Buu, not you!"