The Wretched Sneak is a mini-boss found in a unique chamber in Tartarus. It starts appearing in Tartarus once Zagreus has reached the surface at least once. (Defeating the final boss is not necessary.)
It attacks in a pattern of teleport, jab (7 damage), teleport, darts (3x4 damage), teleport, darts (3x4 damage), repeat.
When Middle Management is turned on, it periodically gathers Wringer reinforcements from the sides of the chamber, potentially swarming Zagreus if he does not take them down.
'...I am unfit to judge those who, in their mortal days, made work of taking lives. In my case, such bloodshed was sanctioned, even honored as a necessary consequence of war. But there are those who took lives for no cause other than personal gain. And now, even in death, they serve the highest bidder. The Master gives them brief reprieve from Tisiphone's whip in exchange for ensuring the other worst wretches of Tartarus remain firmly in their place. They are not permitted to leave their solitary confinement; but should any other soul trespass there, they are all too eager to ply their old trade.'