It is not known to evolve into or from any other Pokémon. It can Mega Evolve into Mega Sableye using the Sableyeite.
It digs branching holes in caves using its sharp claws in search of food--raw gems. A SABLEYE lurks in darkness and is seen only rarely.
(From Bulbapedia) Sableye is a bipedal Pokémon with a dark purple body. It has pale blue, gemstone-like eyes, which allow it to see in low light and sparkle in the dark. It also has a red gemstone on its chest, and its back has a blue and green gemstone as well as another red one. These gem-like eyes and adornments on its body are caused by its diet, which consists of rocks and raw gemstones. It also has sharp teeth and claws.
As Mega Sableye, all the energy from its Mega Evolution is concentrated into the red jewel on its chest, causing it to detach from Sableye's body and significantly increase in size; the detached jewel leaves a small hole in Mega Sableye's chest. Its ears elongate, and it gains a spike on the top of its head. Its teeth turn from white to yellow, and its eyes also change from pale blue to a crimson red, with diagonal slits at their inner edges. The enlarged jewel is said to boast such incredible hardness that no attack can even leave a scratch on it. During battle, Mega Sableye shelters itself behind the jewel, from where it can take advantage of any openings its target leaves exposed.
It is feared by people, since it is said to steal a person's soul if they look into its eyes.
Sableye is the only Pokémon capable of Mega Evolution that has not yet done so with an NPC.
Mega Sableye and Unymph has the lowest base Speed in Pokemon Uranium.
(From Bulbapedia)Sableye is a stylization of the Hopkinsville Goblin, a creature from an alleged Kentucky "alien encounter" described as having shining eyes, small legs, clawed arms and swaying hips (a movement that Sableye does indeed imitate in the 3-D Pokémon games). The Hopkinsville aliens are most famous in Japan, where they have appeared in other anime and video games.
(From Bulbapedia)Sableye is a combination of sable and eye. It may also be a play on able-eyed.