Lowest of the Low is a side quest in Egypt (Act II). It is given by Merab, an old beggar standing at the entrance of the Beggars Quarter, before entering the City of Memphis. He asks you to clear the poor people's homes from the monsters lurking around there.
These monsters are Shadowstalkers, a type of demons, surrounded by a thick black cloud. They are melee fighters with a fairly powerful attack. When they spot you, they quickly approach you while being protected by their cloud against ranged attacks.
Try to fight no more than just a few of them at a time and avoid being surrounded, as this can mean a quick death. Especially ranged fighters and pet masters should be careful with this - attacking a Shadowstalker will cause his nearby friends to chase you down as well. Try to move close enough to have a monster spot you, then lure him away a good distance and finish him off. There are about 15-20 of these creatures. When you have killed the last Shadowstalker, the quest will be updated and can return to Merab to get your reward and complete the quest.
Reward: 8500 experience, random magical ring