Peng is an enemy most frequently found in Frostor.
Alpha Lore (unlocked by killing Alpha variants)
Aerial Reconnaissance Unit.
Amidst the nationwide paranoia that eventually led to the Home Security Freedom Act of 2034, demand for nonlethal, highly conspicuous home-scouting solutions grew and grew until the Industry could no longer ignore it. Hitting just in time for the holiday season of 2032, the first Peng model was the ultimate hybrid children's toy and Home Security scout, capable both of charming young ones with its shrill, awkward cries, and orbiting the perimeter of the child's home while it slept.
Beta Lore (unlocked by killing Beta variants)
With the passing of the first version of the Act in 2034, the Peng's developers gained the freedom to be a little more aggressive with their baby, and so the first Beta Peng came to be. With exquisite perpendicular detection capabilities, this new Peng became capable of turning on a dime when encountering an intruder, and aggressively shuffling it off its defensible property (and possibly also this mortal coil) with its heavy Feetjets and razor-sharp beak.
Gamma Lore (unlocked by killing Gamma variants)
Built entirely to protect perimeters from intruders, this initially-friendly child's toy was high on the Project acquisition list. When the time came to develop the Control Set, the Corp's Department of Truth engineered multiple scenarios where Peng models appeared to injure the home inhabitants they were built to protect, and used the ensuing lawsuits to destroy their initial builder on the cheap, acquiring the Peng production line for a song. They were given to Arlan to use as a birthday present; I suspect he may have a personal connection to the line from personal days long gone.