"Become a goat from outer space!"
Mobile: Grab an energy ring (the energy ring is at the alley four buildings away from the skyscraper) and put into the garage by the river. Then go and get the alien near the UFO and bring it behind the resurrection device. You will become the alien and a goat will spawn (your old self)
Consoles: Get all 30 Trophies in GoatVille.
PC: Get all Trophies in Goat City Bay.
Space Goat plays more or less identically to a standard goat, though it smashes with its eyestalk in place of headbutting and can't propel anything with headbutting.