Aliens

Aliens, also known as extraterrestrials, are creatures that did not originate on Earth. They appear in Grand Theft Auto V as easter eggs and figments of Michael's imagination.

Overview
Their bodies are similar to the Vortiguants from the Half Life series, while their elongated head is reminiscent of the Xenomorphs from the Alien franchise. They have green skin and large mouths with big teeth.

Prologue
The mission guides you to go to ahead over the train rails, instead, turn right and go under the bridge, stop the car, get out, and you will notice that there's a frozen alien in the river.

Grass Roots
Playing the mission as Michael will trigger a hallucination after smoking weed. Michael's vision and hearing become blurred and the world around him appears to be in a haze. He is suddenly hefting a minigun as aliens begin to appear all around him. Michael must defeat the aliens without dying himself.

Did Somebody Say Yoga?
Michael goes along with Jimmy to a Burger Shot. On their way back home, Michael unintentionally gets high from Jimmy's weed. Jimmy then forces his father out of the car, and drives off alone. Michael then hallucinates being surrounded by monkeys, abducted by aliens, and then dropped off midair floating over the city.

Transportation
Main article: UFOs

As a method of transportation the aliens use UFOs, or referred to popularly as "flying saucers" or "flying discs". One appears during the mission Did Somebody Say Yoga?, which is used do experiments on human beings. A sunken UFO can be found at the north of the map at the bottom of the sea. Also, after achieving 100% Completion, an UFO can be seen on top of Mount Chiliad. Oddly, it has "FIB" written on it, which might mean that the agency knows about their existance and even managed to build an UFO by themselves. Different looking UFOs appear in the sky, high above Fort Zancudo and Sandy Shores.

Trivia

 * The man selling weed refers to the aliens as "monsters".
 * Grand Theft Auto V is the first game to actually feature aliens. In Grand Theft Auto: San Andreas they were referenced, but not seen.
 * People with alien costumes appear inside the Majestic Studios, Los Santos.
 * A movie called "Los Santos 2020" features an alien.