He looks like a giant baby and does not speak (except for a really deep "Goo!") He wears a giant cloth diaper held up by a giant safety pin, a baby blue bonnet, a sash that reads "Happy New Year," and carries a giant rattle with him.
Baby New Year is one of several Holiday-themed characters that banded together to get rid of Santa Claus, whom was getting all the attention due to Timmy Turner wishing for it to be Christmas every day. Baby New Year was the muscle of the group. Thanks to Timmy and kids from around the world, they were able to foil the other Holidays' plan and stop it from Christmas happening every day. Timmy, his godparents, and the other holidays then make amends to Santa by doing Christmas for him next year while Santa and his wife vacation in Hawaii.