The Sleeper is a boss found within the Farmstead in The Color of Madness DLC. It serves as the second phase to Fracture, and is guaranteed to be encountered on the wave group after the Miller.
The Sleeper has two incredibly powerful attacks: The Sleeper Awakens and The Sleeper Stirs. Both deal very high damage, target the entire party and inflict major stress in some way, either directly or through Horror. It has an equal chance to use either on any given turn, and since both attacks target the whole party there are no weights for targeting selection.
Its high HP and 30% PROT make fighting the Sleeper a test of endurance. Its Bleed Resist is quite high (though not immune like Bone enemies or the Miller), but its Blight Resist is below average, making stacking powerful blights with multiple heroes like the Plague Doctor or Shieldbreaker potentially viable.