Clad in tattered robes, these wretched husks of captured sorcerers scuttle hunchbacked through the streets of Malifaux at the behest of the Guild. Subjected to the tender mercies of the Witch Hunter Task Force, these poor creatures have had the magic they once wielded turned against them, the eldritch energy now anathema to the human form. This has a threefold effect; the first is that Witchling Stalkers' bodies and souls - not to mention the vicious runic blades they carry - are in a permanent state of entropic decay, to the point that they even corrupt those that they touch; the second makes the Stalkers living "homing missiles" of sorts, able to track down soulstone users with unerring accuracy in order to bring them to the Guild's justice; lastly, Witchling Stalkers become nearly impervious to magic of any kind, and are even capable of draining the power from enemy mages.
Unfortunately (or perhaps not, the Guild may have designed them this way on purpose, and has certainly done worse in it's time), when a Witchling Stalker is blessed with release from it's torment by death, it's pent up energies are released and it explodes. Obviously, this is not particularly healthy for those in the Stalker's vicinity.
Witchling Stalkers were first created by Guild Master Sonnia Criid to aid her in hunting down and capturing rogue Arcanists, but since their inception have gained more widespread use in the Witch Hunter Task Force. Indeed, specialist Witchling Handlers have been trained to operate Stalkers on missions where Criid is not present.