Puf
From Kerbal Space Program Wiki
Puf would have been a small planet that has been nicknamed the "Eyeball Planet". Judging by pictures of this little space rock, it looks to be close to the size of Duna. It was theorized to be in the Tuun System.
Surface
Most of Puf's surface is covered by brownish rock, with the poles having major ice caps. However, Puf is mostly known for the huge crater sea on its surface. It's unknown why it has this giant ocean, but one theory is that a proto planet collided with Puf, resulting in a giant crater. Another theory is that it would have been an "eyeball planet", a planet tidally locked to its host star causing most of the temperature to remain in one spot. There are no confirmed moons.
Atmosphere
Puf has a thin, blue atmosphere similar to Kerbin.