The Sun Baby is the sun of Teletubbyland that shines in the sky and makes baby noises, appearing as an Assist Trophy in All Star Smashers. When summoned, she covers the screen, which blinds CPU's, similar to Captain Underpants's Neutral B.
In various episodes of Teletubbies, the Sun Baby will appear on-screen for 5 seconds after a scene has ended, in which she mostly just laughs at what had just happened. She is also seen in the Intro and Outro to every episode.
The Sun Baby was revealed as an Assist Trophy before The Teletubbies appeared in the second All Star Smashers Empty Slot.