The Aliens are members of the Imperial Armada in the Back at the Barnyard Episode: Aliens!!!, the Final Episode of the show's series.
Appearance[]
All the Aliens presumably share a common biological structure. They have three eyes, one central eye on the head and 2 eyestalks on their sides. They have protruding slender necks, round plump bodies, and various cilia-like structures around their necks, backs and bodies similar to Chode McBlob from Tripping the Rift.
Their Color skins are Vibrant and Neon, ranging from purple to orange. They also wear rings on their necks, presumably for jewelry or clothing, but some wear their outfits, and have hair as shown by Kirk and Scotty Aliens.
They are species of planet conquerors with no name inhabited by an Unknown planet far in outer space. They were accidentally contacted by the talking cow Otis's Deep Space Satellite, believing that Otis and his barnyard pals were actually aliens, but they were planned to conquer earth themselves before they could.
Weaknesses[]
Their sole weaknesses are Milk or other fluids. However, their bodies dissolve upon contact and presumably the only substance than can cause the Aliens' Physical Harm. Enough Milk would kill them, but the most of it was shown to do is reduce their bodies into gelatinous forms. 
They Also are Weak to the heat radiation by staying in the sun for a really long time. They can melt and eventually get cooked alive in which they can start evaporating to death.
Miscellaneous[]
Most of the Aliens' Power comes from Advanced Technology, including laser ray guns, Spaceships, Tractor beams and so on. However, Ships and Ray Guns are equipped to destroy or rearrange matter on different planets.
Weaponry[]
Ray guns are also capable of freezing enemies in carbonite a la Star Wars. The Aliens are also capable of manipulating biological systems. Life as shown by Nora's disembodied but conscious head and her later rearrangement of her limbs.