Blood Warden is a KillerPerk. It is unique to The Nightmare until 40, which it can then be taught to the other Killers.
Perk Level 1
Perk Level 2
Perk Level 3
Once per match, once at least one Exit Gate is opened, hooking a Survivor summons The Entity to block the exits for all survivors for 30/45/60 seconds. While Blood Warden is active, auras of survivors located within the Exit areas are revealed to you. “This is my world. And you can’t ever leave.” –Freddy Krueger Unique to Nightmare until level 40, which its Teachable version can then be learned and taught to the other Killers