Aliens are relatively small, green yellowish-skinned humanoid beings with no primary sex characteristics. Their bodies are elongated with a small chest, are lean and lack any muscular definition. They also display no body hair of any kind. Their legs are shorter and jointed differently than a normal human and their limbs are also proportionally different than a normal humanoid; their humerus and femurs are the same lengths as their forearms and tibias.
Their heads are unusually large in proportion to their bodies and no noticeable outer ears or noses, instead only having small orifices for ears and nostrils. They have very wide mouths, no teeth, a light green tongue and large opaque black eyes with no discernible iris or pupil. Their hands have only three long suctioned-cupped fingers and no thumbs, however their fingers are so long they can wrap around objects and use any objects like any other humanoid species. They seem to breathe a similar atmosphere that humans do and process nutrients through the body with green blood. They subsist on a diet of unknown worm and squid food.
Most aliens encountered are either hostiles or workers. Hostile aliens sometimes have shields which boost their damage resistance significantly. In combat they tend to hang back or rush the player if they are using melee weapons.
Regular aliens are the most common alien the player will see aboard mothershipZeta. They act as the standard enemy of the area and will always be hostile towards you. Aliens have many tiers, depending on the players level. Tiers 1-3 do not have an inertia suppression field and the aliens tier 4-6 do. You can tell an alien has on an I.S.F. because their bodies will shimmer and become slightly distorted.
† The inertia suppression fields protection depends on the level of alien using it.
The alien captain is the leader of the alien forces on mothership Zeta, equipped with a modified alien blaster and a shiny grey space suit. Despite being the leader of the Zeta's aliens, his stats are the same as the lowest-ranking aliens in the game, and his weakness in combat is compounded by his lack of an inertia suppression field. As the ship's captain he has remote access to the mothership's shield and death ray power systems, and a big button in front of him, which can fire the death ray.
Alien workers are the working force of the mothership Zeta. Although displayed as hostile, they will never attack the player, but will flee or cower in fear instead. Killing one results in minor Karma loss although this may not be the case if you are not directly involved such as overloading the assembly when they are near it. During the quest Not of This World, when you first spot them, Sally will tell you not to hurt them because they are harmless.