"How blithely you use the word alien; you have no idea how alien a thing can be."
― The Dark Side of the Sun, Terry Pratchett
"This planet is the home to the largest mass of organic creatures ever seen. What breeds down in the pits of the planet is unknown and unrecognizable, but can be purchased for a low price at Woboo: Land O' Meat."
User with this ability either is or can transform into an extraterrestrial/alien: life forms that are of extraterrestrial origin. Given the near infinite variety of possible extraterrestrials, even only the ones in fiction, a user can conceivably use nearly any power.
Gain the form of extraterrestrials from fables.
Possess any special abilities of extraterrestrial creatures.
The Royal Four (Roswell) have this ability due to their alien ancestry
Despite looking like a human, The Doctor (Doctor Who), is an alien called a Time Lord.
Martians or commonly known as Ice Warriors (Doctor Who)
The Asgard (Stargate franchise) were a benevolent, extremely advanced race from the Ida galaxy that visited Earth on many occasions. They used the cover of primitive gods in a similar manner to the Goa'uld, leading to the development of Nordic mythology.
The Goa'uld (Stargate Franchise) are a race of sentient parasitic beings that take over hosts.
The Wraith (Stargate Atlantis) are a vampiric hive-based species that harvest the 'life-force' of other humanoid beings for nourishment through suckers on their right hand palm.
Unas (Stargate SG-1) is a race named by the Goa'uld that translates to 'the first ones' or 'the first race' or more specifically, the first humanoid race that they used as hosts before Ra discovered Humans on Earth.
Cole/Daggon (Tracker) is a member of a species of energy-based extraterrestrials known as 'Cirronians'.
The Blancmange (Monty Python's Flying Circus) are a race of extraterrestrial, sentient blancmange that turn the UK's population Scottish so that they could win wimbledon.
The Legion of Super Heroes (DC Comics) is a 30th Century inter-galactic team of super-powered young adults. This cast expands to include dozens of members with a diverse array of powers and personalities.
Saturn Girl (DC Comics) hails from Saturn's moon Titan, where everyone is a naturally born telepath.
Garth Ranzz (DC Comics) also known as Lightning Lad or LiveWire hails from the planet Winath, where twin births are ubiquitous, accounting for almost all natives of the planet.
Cosmic Boy (DC Comics) hail from the planet Braal, where everyone has the natural power to manipulate magnetic fields
Lar Gand (DC Comics), better known as Valor or Mon-El is a Daxamite, the distance cousins of Kryptonians.
Star Boy (DC Comics)
Andromeda (DC Comics)
Shrinking Violet (DC Comics) hails from the planet Imsk, where everyone has the natural ability to shrink down to sub-atomic sizes.
Kal-El/Superman (DC Comics), a Kryptonian, is perhaps the most well-known alien today.
Kara-Zor El, Supergirl (DC Comics) the Girl of Steel is also a Kryptonian.
Power Girl (DC Comics), another female Kryptonian.
Kryptonians (DC Comics)
The Guardians of the Universe (DC Comics)
The Burning Martians (DC Comics) were the dominant life form on the planet Mars before being genetically altered by the Guardians of the Universe.
Green Martians (DC Comics)
White Martians (DC Comics)
J'onn J'onzz, the Martian Manhunter (DC Comics) Mars's greatest son.
Tamaraneans (DC Comics)
Blackfire (DC Comics)
Starfire (DC Comics) is an alien princess from the planet Tamaran with powers of flight and energy projection.
Daxamites (DC Comics)
Dominators (DC Comics)
Braalians (DC Comics)
Carggites (DC Comics) have the natural ability of Bio-Fission allowing the split their physical form into three independent bodies.
Kilowog (DC Comics) hailed from the planet Bolovax Vik, which was one of the most crowded worlds in the universe; it had sixteen billion residents with a communal mind.
Icon's (DC Comics) lifepod altered his DNA so he would resemble a normal human being, thus enabling him to blend among Earth's natives.
Mongul the Second (DC Comics)
Mikaal Tomas (DC Comics), better known as Starman.
The Sinestro Corps (DC Comics)
Atrocitus (DC Comics)
Skrulls (Marvel Comics)
Kl’rt, The Super Skrull (Marvel Comics)
A Badoon (Marvel Comics)
Dire Wraiths (Marvel Comics), a magical offshoot of Skrulls.
The Shi'ar (Marvel Comics)
The Shi'ar Imperial Guard (Marvel Comics)
Noh-Varr (Marvel Comics) a pink skinned Kree.
Techarchy (Marvel Comics), a techno-organic species.
Eclipse the Darkling (Archie's Sonic the Hedgehog), a black arms alien.
Ceneca-10050 (Archie's Sonic the Hedgehog), a bem alien.
Utrom (Teenage Mutant Ninja Turtles)
Composite Man (DC Comics)
Viltrumites (Image Comics)
In her original origin story, Vampirella (Vampirella) was a member of the Vampiri species, an alien race from the distant planet Drakulon with identical powers to the vampires of human mythology.
Alien Grunts (Hλlf-Life series) are a group of Xen Aliens considered being stronger than Vortigaunts. They don’t exactly have the power to manipulate myriad energy at all, but instead, they use Hivehands, weapons that can spit out Hornets.
Headcrabs (Hλlf-Life series) are extraterrestrial parasites, though at least they tend to be for the sake of protecting themselves from greater predators. Thanks to having hidden beaks, they have a really strong bite, and they use them to graze through the human skull and take control of their nervous systems, turning them into Zombies.
Ichthyosaurs (Hλlf-Life series) are shark-like Aliens that roam inside the waters of Xen, and in terms of behavior, they are considered to be predatory like Sharks. They are fast swimmers, and trying to escape them is possibly doomed to fail. Thanks to having sharp teeth, they have an extremely powerful bite.
Snarks (Hλlf-Life series) are aggressive but small Xen Aliens. If there is only one Snark, they are ridiculously easy to kill, but once they form a herd, they will manage to kill their enemies in possibly seconds.
Like the rest of Xen’s inhabitants, the Tentacles (Hλlf-Life series) are extraterrestrial creatures that are found in the Borderworld. They are tall, and dangerously savage Aliens that can viciously attack anyone that happens to make sound within their vicinity.
Vortigaunts (Hλlf-Life series) were forced into aggressive slaves by the Nihilanth, but after his death, they became allies that have fought alongside the resistance against the Combine.
Race X (Hλlf-Life: Opposing Force) is an Alien race that can be considered rivals to the mainstream Xen Aliens. Their primary goal is to assimilate the entire world by force, which the Gene Worm is focused to do.
Hydras (Hλlf-Life 2) are commonly located and fought in the sewers. Each of their heads is shaped differently for different purposes, while the main head is used to pierce targets.
The Combine (Hλlf-Life 2 series) is a powerful extraterrestrial empire that had successfully taken over the planet Earth after the Black Mesa incident.
Shadow the Hedgehog (Sonic the Hedgehog)
Black Arms (Sonic the Hedgehog)
Wisps (Sonic the Hedgehog)
Draenei (Warcraft) are a race of intergalactic beings that came to Azeroth to aid the Alliance.
The Protoss (Starcraft) are a race of Psion beings that have conquered many worlds with their vast technology.
An Asari (Mass Effect)
A female Turian (Mass Effect)
A Krogan (Mass Effect)
A "Leviathan" (Mass Effect), the oldest known intelligent race in the Milky Way.
A naked Sangheili (Halo)
A Jiralhanae (Halo)
A San'Shyuum (Halo)
A Mgalekgolo (Halo)
Deoxys (Pokémon), one of the few confirmed extraterrestrial Pokémon.