A group of Sectoids

"Aliens" (often referred to as "X-Rays" by the soldiers) is the human term used to collectively designate the extraterrestrial enemy force that invades Earth in 2015 under the direction of the Uber Ethereal.

They are the main antagonists and enemies in XCOM: Enemy Unknown.

Alien types[]

XCOM: Enemy Within[]

This expansion adds two new aliens types:


The aliens' technology initially outstrips anything available on Earth, including XCOM's in-house development; however, the technology gap is bridged quickly as XCOM's operations yield captured artifacts of increasing sophistication.

Small Arms[]

The Aliens wield potent plasma weaponry.

The aliens rely on several variants of plasma weaponry ranging from the wrist-mounted Sectoid pistols to the Elite Muton's massive plasma cannons. These variations boil down to the same four basic weapons of increasing power and size:

However, the aliens lack specialist weaponry for either long-range marksmanship or close-range assault but conceivably they have the ability to produce such weaponry as proven by XCOM's rapid development of the Plasma Sniper Rifle and Alloy Cannon designs. For additional assault firepower, elite alien troops use Alien Grenades, which are more powerful than their human equivalent, yet have the same blast radius. All alien small arms are set to self-destruct after their user's death, although they may leave behind Weapon Fragments which can provide basic insight into the technology.

Melee Weaponry[]

Berserkers possess wrist-mounted blades for extra damage, although the creatures themselves are dangerous enough.

Chryssalids are living weapons themselves, ripping their targets to shreds with their poisonous claws or implanting their victims with their eggs.

The Zombie, an intermediary between a healthy humanoid and a (newborn) Chryssalid, is a surprisingly sturdy and similarly medium-heavy hitting monstrosity.

Seekers (EW) are floating cloaked isolator hunters who disrupt your squad construction and gameplay planning. They use a unique weak, continual strangulation martial concept which is most dangerous if you are not prepared to deny it while dealing with others.


The aliens have never been observed using manned ground vehicles but instead rely on advanced robotic units for support.

The Cyberdisc is questionably a living creature encased in a thickly-armored transforming shell, equipped with an anti-grav unit and armed with a deadly cannon.

The tougher and more powerful Sectopod is a bipedal robot which is armed with a powerful primary cannon and a back-mounted defensive plasma gun.

Additionally the aliens field flying Drones which primarily escort the larger robots and can perform field repairs on them as necessary.

In XCOM: Enemy Within the aliens deploy two additional robotic units.

Seekers will use stealth to ambush and strangle soldiers.

Mechtoids are Sectoids in big cybernetic suits armed with plasma cannons; Mechtoids are usually accompanied by other Sectoids or a Sectoid Commander.

Psychoactive Technology[]

This area remains poorly investigated. However, it is known that some alien devices are designed to be interfaced with by psionics such as Sectoid Commanders or Ethereals.

Aircraft and Spacecraft[]

An Alien UFO bombards a city.

The aliens' access to superior hull materials and advanced subsystems such as Elerium-based Power Sources and sophisticated Flight Computers gives them a colossal advantage in aerial power. XCOM Raven interceptors cannot maintain prolonged contact, even without considering the UFO's armaments.

All identified UFO types are larger than XCOM interceptors.

Known UFO Types[]


Alien ships appear to use Plasma Cannons, whereas the Battleship carries the mighty Fusion Lance, which is significantly more dangerous than its miniaturized XCOM derivatives.


It appears that the Uber Ethereal wants to subjugate the human species while acquiring some of the finest, most psionically-gifted specimens.

To carry this out, the aliens begin space-borne intrusions on Earth rather than an all-out apocalyptic assault, initially aiming to abduct random civilians to carry out basic experiments. After the XCOM response becomes tangible, the force begins conducting overt "Terror Missions" in populated areas as well as relying on various other means of raising worldwide panic that seem to aim to undermine support of XCOM. However, the Ethereals keep leaving clues that finally bring the most able, most psionically gifted human onto their capital ship.

Species Deployment[]

With the exception of ship commanders, new enemy units begin to be deployed by the alien forces according to a fixed schedule (see table, below). Species that are introduced in the early and mid-game are generally most predominant during the first one to three months that they appear. Early-game species such as Floaters drop to a very low chance of deployment (circa 2.5%) by late-game, but are never removed from the pool of available aliens. Outsiders are an exception, as they no longer appear following the Alien Base Assault mission.

Operation Progeny and Slingshot DLC missions do not adhere to the schedule and may include aliens before they are regularly deployed (e.g. Mutons can appear in Slingshot missions before May). Similarly, Ethereals may be encountered during the XCOM Base Defense mission in Enemy Within. These occurrences are unique, and do not prematurely commence the appearance of these aliens in other missions.

Within the first seven months all of the non-commander alien species are deployed during regular gameplay. The appearance of new aliens is delayed if the "Marathon" Second Wave option is enabled, indicated by a month in brackets in the table below.

Soldier / Secondary Units
Month Alien(s)
01 - March Sectoid

Thin Man

02 - April Floater



03 - May
(04 - June)



04 - June
(06 - August)
05 - July
(08 - October)
06 - August
(10 - December)
Heavy Floater
07 - September
(12 - February)
Muton Elite
Mission Alien(s)
Alien Base Assault Sectoid Commander
Overseer Crash Site Ethereal
Temple Ship Assault Uber Ethereal

Stat Comparison[]

Stats based on Normal difficulty:

Enemy HP Def Aim Crit% Mobility Will Weapon
Berserker 20 20 - 0 17 80 Muton Blade
Chryssalid 8 10 - 0 20 120 Chyrssalid Claw
Cyberdisc 16 10 70 0 18 - Plasma Cannon, Alien Grenade
Drone 3 10 60 0 12 - Drone Beam
Ethereal 20 40 100 0 12 120 Psionic Lotus
Floater 4 0 50 0 12 10 Light Plasma Rifle
Heavy Floater 12 10 70 0 12 25 Plasma Rifle, Alien Grenade
Mechtoid EW 20 10 70 0 14 - Plasma Mini-Cannons
Muton 8 0 70 0 12 10 Light Plasma Rifle/Plasma Rifle, Alien Grenade
Muton Elite 14 20 80 0 12 20 Heavy Plasma, Alien Grenade
Outsider 3 0 70 0 12 20 Light Plasma Rifle
Sectoid 3 0 65 0 12 10 Plasma Pistol
Sectoid Commander 10 20 85 0 12 90 Plasma Pistol
Sectopod 30 30 80 0 12 - Chest Cannon, Cluster Bomb
Seeker EW 5 10 65 0 14 - Plasma Pistol
Thin Man 3 0 65 0 15 15 Light Plasma Rifle
Uber Ethereal 25 40 100 0 12 150 Psionic Lotus
Zombie 10 0 - 0 8 120 Zombie Fist

Aliens are subject to a variety of bonuses and penalties that modify their stats during combat.


  • Any alien that is not Hardened should be able to use the Hunker Down ability, but cannot due to a bug in the XComGame.upk game file. This can be fixed using a hex editor to manually change data in the file. Details can be found in The Nexus Forums, here. Hunker Down can be a random behaviour for panicked aliens (and humans).