Demons are a powerful humanoid race of monsters in Goblin Slayer.
Demons are the common enemies of all other Prayer characters. They are led by one person titled the Demon Lord together with his loyal generals.
Lesser demons are aerial combatants that possess batlike wings and curved claws. They may take to the skies and dive down to make an attack with their extremely sharp claws, or may cast magic (such as firebolt) upon their foes. They are very nimble in the skies, making it difficult for even an elven archer to shoot one down. Despite being lesser, they are still demons, thus are still quite strong and not to be underestimated. 
Greater demons are massive muscular creatures with blue-black skin that possess enormous amounts of magical power. Such is their magical power that they cannot be silenced by any but the most experienced casters.  Even if one were to somehow silence their magic, their physical abilities still pose quite a threat, with fists as large as a giant's able to punch through walls.  They make meals of humans they kill, whether they be men or women.