Demon

Demon is a new mob found in the underworld. They were added in 1.0.5. They shoot purple blades at the player, similar to the Demon Scythe spell, in volleys of four. The blades can be destroyed if they are hit by a weapon, like the fireballs of the Fire Imp. Demons that come in contact with lava will not get hurt ( like most underworld mobs ). A variation on the Demon is the rarer Voodoo Demon.

Drops

 * Demon Scythe: 2% (1:50 chance)
 * Around 340

Trivia

 * The Demon's Demon Scythe attack is the only Magic attack produced by an NPC that does not pass through walls; however, the projectile is so big it can, in fact, hit players through one-block thick walls (This is likely a bug [think about the projectile as the center point in a hit box shaped as a 3x3 grid. This way you can fire while standing on flat ground without the projectile immediately impacting on the ground.]).
 * Possibly a reference to the demons from the Jill of the Jungle series. Demons in the series were devil looking enemies with wings that shot circular projectiles with a similar look to the scythes shot by the Demons in Terraria.