A group from Cainhurst Castle.
They are born of forbidden blood that was stolen from Yharnam.
The Cainhurst Vilebloods are a covenant in Bloodborne. The focus of the covenant is on PvP and invasions.
"Pledgers to this oath are Cainhurst Vilebloods, hunters of blood who find dregs for their Queen of coldblood, particularly in that of hunters. Yet the corrupt are heretics in the eyes of the Church, thus subject to the wrath of the Executioners."
To join the covenant, you must talk to Annalise, Queen of the Vilebloods and agree to join the covenant. The Caryll Rune for the covenant is Corruption.
Members are ranked on the Vileblood Register based on how many Blood Dregs they've donated. Blood Dregs are found by killing other hunters, either NPC or player, while the Corruption rune is equipped. What rank you are on the Vileblood Register has no in-game effect. Upon joining the covenant, members receive the Corruption Rune, the Cainhurst Badge, and the Respect gesture. After donating 1 Blood Dreg, the player gets the Deep Respect gesture. Blood Dregs can be consumed for 1 insight.