"The Leech will see each patient only once; after treatment, there will be a recognizable mark upon the patient, and the Leech will recognize his or her handiwork without fail."
- from the writings of Erbius the Loremaster, Magus of the Fifth Order
"...apparently she had brained the thing with a heavy chamber pot from the loft. It left quite a mess, to be sure. I can't be certain, but it looks (and smells) like another of those stitched walkers from last month. I found several of those circular festering wounds; furthermore, the jaw mostly survived, and the lips were indeed sewn shut..."
"...I'm just wondering who makes the things. Obviously they're not stitching up their own mouths, eh?"
- Cramel of the Watch, to his superior officer
Use the Leech in your games. If the PCs spend any amount of time in Evandra (or, rather, a city of your choice), they will hear rumors of the Leech and his/her remarkable medical ability. A useful resource for dangerous games where health and limb are at risk!
However, any character who finds the Leech and receives treatment will have a parasitic organism inserted near their brainstem during the (very private) procedure- difficult to detect, and even more difficult to remove. This "leech" degrades the character's constitution (or maximum health or whatever) by one point each winter. When the character dies and the corpse is quiet and alone (perhaps abandoned, perhaps buried), the parasite causes the (un)dead body to animate and return to the Leech as a particularly durable and tame zombie (or equivalent).
What purpose could the Leech possibly have for such reanimated abominations?
For a week, I'm challenging myself to write SOMETHING gameable (monster, NPC, magic, location, item, etc.) each day. To make it interesting: it must be inspired by the first song that comes up on shuffle from my music library each morning. This is post 2, inspired by "Leech" by Sylosis (Spotify, YouTube).