Some people suspect that BEHEEYEM, CLEFABLE, and S51-A are conspiring to invade the planet. No one is safe.
S51-A is a large extraterrestrial being. It appears to be a round dark-green creature with two pointy ears and dark-green markings adorning its face, which has two large eyes, one red and one blue. Its body is composed of a metallic UFO with a glass dome on top, and a metallic purple bottom with yellow stripes and multicolored lights. It has two large purple arms protruding from the bottom, with yellow palms.
As Mega S51-A, its face slightly changes shape, and its body becomes rounder and larger, closer in shape to a lunar lander, with two laser cannons on top and resting on four thick yellow arms with purple markings.
S51-A is known for being good at commanding S51, and can also fire a laser that can deal Fire, Ice, or Electric qualities (Laser Pulse).
S51-A is the alpha of S51, and as such is able to command a group of S51 to its will.
S51-A is a Pokémon rumored to originate in outer space. Its actual origin and habitat is unknown.
As of version 1.2.2, if S51-A is encountered outside of its normal location during Randomizer Mode, it is able to be caught as with any other Pokémon (catch rate 45). The same is true for Seikamater (catch rate 15).
If the Mothership Form is completed and added to the game, S51-A would be the only Pokémon in Pokémon Uranium with 2 Mega Evolutions.
Its main form is probably derived from the many UFO sightings compiled into one. The flashing multicolored lights and the green alien inside with large eyes were the main source of paranoia in the mid-1900s.
The aesthetics of aliens in pop-culture was likely also the inspiration for the decision to alter the shiny version's color palette. As many modern stereotypical depictions of extra terrestrials tend to have gray skin.
Its name consists of the letter "S", the number "51" , and the letter "A". The "S" is an abbreviation of the word subject, the "51" refers to Area 51, and the "A" stands for alpha, as it is seen giving orders to S51.