Abomination of desolation!
Phantom! A child class of Reiver.
He has less hit points than his older brother. 100 instead of 150. But he is faster and nearly blends with the darkness.
His attacks are a more powerful life leech and ability to fire 6 serpent staff poison projectiles in rapid rate at unprepared player.
Phantom cannot be tracked by seeker missiles, he cannot be blasted by Discs of Repulsion, he does not bleed and he cannot be frozen.
His younger brother Stalker has 95 health points, greater speed and greater life leech damage. Shares same immunities with Phantom, plus he is more darker so that he can blend in with the darkness.
Stalkers attack in melee only and make no noise at all. Making them harder to spot.
This should give you an idea of what kind of foes I like to make.