Type: Dark/Ghost
Classification: Darkness Pokémon
Height: 1'08"
Weight: 354.9lbs
Ability: Magic Bounce
Sableye has concentrated all of the energy from its Mega Evolution into the red jewel on its chest, which increases in size and detaches from its body. This enlarged jewel boasts incredible hardness, and it is said that no attack can even make a scratch on it!
After Mega Evolving, Sableye's Defense and Sp. Attack stats both get boosted significantly. There's a tradeoff however, since its Speed stat decrease slightly. Fortunately, it has a Magic Bounce Ability that reflects any moves that affect only stats or Status Conditions back to its user.
Reference and images: Serebii.net
Additional references, images, and information: pokemonrubysapphire.com