The Alien, as it is commonly referred, is a Xenomorph, originating from the film Alien, and its sequels and adaptations. It appeared in the Season Eleven episode, "Imaginationland, Episode II".
Background
The Alien is one of many characters and creatures from popular culture that is represented in the Imaginationland series of episodes. As the main antagonist of the Alien film franchise, the Alien in Imaginationland is also antagonistic. It is killed by Jesus wielding an M60, previously his sword, after Butters uses his imagination.
Appearance
The Alien is mostly blueish-black in appearance, mostly. It is a facultative biped, walking on hind legs and running on all fours. It is thin, almost skeletal, bio-mechanical in appearance. They have elongated skulls with no distinct facial features other than a mouth concealing its pharyngeal jaws. Along the back are four dorsal tubes, an upper and lower pair, with a sharp spine separating them that runs the center of the torso.[1]
Weapons
The Alien uses its body as its main weapon. Along with the biting of an enemies head with its pharyngeal jaws, the Alien will also use its clawed talons, or blade-tipped tail. As if this wasn't enough, The Alien also has acid for blood.