Quell

The Quell is a horrific tentacled creature that appears as a boss in The Evil Within. This monster possesses an amalgamation of human, octopus and lamprey-like qualities, sporting numerous tentacles, two human-like arms and a head with the hideous maw of a lamprey. Like most of the creatures in the game, the Quell represents a certain aspect of Ruvik's psyche, namely his desire to go unseen by others. This trait is evident by the Quell's ability to turn invisible.

Gameplay
The Quell makes its first appearance in the sewers of Krimson Subway throughout Chapter 14: Ulterior Motives, where it is seen on several occasions sneaking up on unwary AlterEgos, though it tends to stay hidden in the background. It isn't after until the dark, gunk-mired corridor with iron grating before the final fenced off operation area in the sewers that the creature finally decides to reveal itself, initially masking as the crank generator used to power up the exit elevator, the creature remains hidden until Sebastian Castellanos comes over to restart the device, at which point it reveals its true form and tossing the detective down into a nearby pit where it is fought.

Damaging the creature enough will make it cloak and hide somewhere to lure Sebastian towards it, at which point it will seize him and attempt to perform an instant-kill move. Though invisible, the creature's location can be pinpointed with its hissing and the drool that constantly drips from its mouth. During this phase, the Quell may also release writhing slug-like spawns that hone in on Sebastian and implode, causing much damage and potentially knocking him down.