Baby Character Facts

Seemingly created as a "last resort" by the demented Machine Mutant Dr. Myuu, Baby is a parasite whose purpose for living is to see through the annihilation of the Saiyan race and domination of the universe in the name of the Tuffles. However, as his name implies, Baby is highly immature and is prone to fits of rage and panic, as well as not taking his battles seriously.
Initially, Baby is single-minded in reviving the Tuffle race and exterminating the Saiyans. Over time, it is shown that he is cunning enough to dominate the Z Fighters, possessing Vegeta and successfully restoring the Tuffles' home planet. However, Baby is also incredibly childish and immature; he is very prone to taunting, and flies into a rage if he is teased enough. Ironically, despite seeing the Saiyans as a barbaric race, he displays enjoyment in battle as well; upon becoming a Golden Great Ape, Baby pretends that he is on a mindless rampage (which is a common occurrence among Great Apes and Golden Great Apes), and massacres countless followers as a means of testing out his abilities. He is very intelligent, and has an extremely egotistical and selfish personality. 
In his initial form, Baby is very small and must crawl as a form of movement, like a baby. At first, he seems very simple and easily takes orders from Dr. Myuu. Afterwards, however, he becomes self-aware and very intelligent. On his own, Baby is no match for Vegeta and the others. When liquefying, he becomes a thick and silvery ooze capable of partially emerging from the body of his host.
Shortly after he is revealed to have survived his first encounter with the three Saiyans, Baby invades Trunks' body for a brief period of time, attacking Goku and Pan, before separating, having implanted a mind-controlling egg within Trunks. The only physical change is his eyes are outlined in black. 
Baby's physical body assumes its first transformation, taking on a more mature appearance and carrying shoulder pads. He also becomes fairly stronger, but is still unable to fight any of the Saiyans one on one. In this form, Baby also becomes more adept at utilizing his liquefied state, even to the point of being able to shift through energy waves, as well as possessing people much more efficiently. 
Upon becoming a teenager, Baby takes control of Goten, who he is content with possessing until Gohan appears. Baby does not hesitate to take action, and engages Gohan in battle, during which he is successful in passing into Gohan's body, but not before leaving a mind-controlling egg within Goten's body. The only physical change is his eyes are outlined in black. 
While in possession of Gohan's body, Baby briefly fights Piccolo. Baby seems confident when he engages Vegeta in battle but Vegeta quickly begins to best him. However, thanks to a possessed Goten, Baby is able to take control of Vegeta. Again, before taking control of Vegeta, Baby leaves an egg planted within Gohan. The power of Baby Gohan is second only to the parasite's Baby Vegeta transformations. The only physical change in his eyes are outlined in black.