A baby. He wears yellow clothes and yellow gloves. His eyes are red, and he can evolve. When evolved, strange eyeballs appear within his eyes, and he can fly, levitate surrounding objects, and toss furniture into the air. Despite appearing as a newborn or infant, he possesses these powers. He hates it when Guest tries to escape. Furthermore, in the Pickman, Escape, Laboratory, and Clash of Worlds stages, he grows larger. Tentacles sprout from his lower body, and his face transforms into a monster. Fleshy, yellow-tinted wings sprout from his back (though he cannot fly with them). He comes to devour people. He is a god-tier demon. This baby often acts like a normal infant to appear ordinary to Guest and others. He is a demonic entity. He can change the atmosphere instantly, turning walls, ceilings, and floors red and filthy, and darkening the area by about 10%. His personality is evil and cruel. He terrifies people and induces phobias. He has no weaknesses.

A cat doll (a doll the Baby in Yellow likes). Kind-hearted.

A rabbit doll (a doll the Baby in Yellow likes). It helps Guest escape and hates the Baby in Yellow. Kind-hearted.

A sheep doll (a doll the baby likes). Kind-hearted.

His name is Newt, a robot that manages and grows plants. He usually appears in the Cat Part. He hates the Baby in Yellow and likes Guest. He can fly if he has boosters, but cannot fly without them (which causes issues with his lower body). If the battery holder in his chest is broken, damaged, or missing, he shuts down (causing issues with his chest). Without ink, he cannot draw or communicate (causing issues with his head). Newt gets scared when the Baby in Yellow evolves or levitates objects. Kind-hearted.

His name is Black Cat. He is an animal, a cat. His body is black, and he usually appears in the Cat Part. He can teleport. He runs away immediately if Guest gets close. Kind-hearted.

His name is The Doctor. This person appears in the Escape stage of the Rabbit Part and the Clash of Worlds stage of the Cat Part.

A baby identical to the Baby in Yellow. Usually appears in the Crown Part.

The eyes of the Baby in Yellow. Eyes within eyes. The black swirls on the outside represent veins and dark energy, while the yellow swirl closest to the eye is the light acting as the pupil. There is a white circle (pupil) in the center, and the red emitted from the pupil is the eye-light. It speaks with the whispering voices of demons. The whispers sound like many people overlapping, making it hard to understand what is being said. It usually whispers things like 'Obey', 'He is watching', 'do not leave', 'stay', 'feed him', 'Put a diaper on him', 'put him to sleep', 'turn him into a more cruel person' all at once. If the babysitter touches it 2 to 4 times, a jump-scare screen of the Baby in Yellow suddenly appears. Guest collapses, and a black screen appears with the text: 'You have seen too much. It kills the curious cat. Turn around and close your eyes. Carcosa is waiting.' Then Guest wakes up again (in the past, Guest would have died).