- "There's a leak... Pissing down on us. Water takes everything apart... down on us. Up from the sewer, that puts us... Water and time could drill a hole in anything."
- ―Dennis, shortly after Waylon drops through the ceiling.
Dennis, referred to as Dissociative Dennis in a document, is a patient at Mount Massive Asylum and a minor antagonist character in Outlast: Whistleblower. He appears only once in the game in a condemned building just above the Vocational Block, where he presumably resides.
Dennis is diagnosed with a mental disorder called Dissociative Identity Disorder (DID), or Multiple Personality Disorder (MPD). He has four expressed identities or personalities: a brother named Timmy, an older brother with a thick speech impediment, their father and their grandfather. All four personalities are active at once and will openly converse with each other, often referring to a life threatening flood. However, whether this flood is a foretelling of a future event or had occurred in the past has had yet to be confirmed. It is suggested that malingering, or a fabrication on reality is the cause for this delusion.
Upon entering the Vocational Block, Dennis can be viewed through a paneled wall, his four personalities conversing over varying subjects. As Waylon Park continues further, he will hear Dennis discussing a plan to use a 'goat' as a sacrifice for Eddie Gluskin, mentioning his hopes to avoid castration at Gluskin's hands. The "father" hints that they have given numerous men to Gluskin to "cut up" in order to save themselves.
Later, Dennis discovers Waylon and considers him to be a suitable sacrifice, before a resulting chase ensues. Waylon escapes by descending to the lower floor, unaware that Gluskin had taken refuge on the third floor. As he exits the fourth floor, Dennis' personalities will individually taunt him and state that Gluskin's 'bride' approaches. Dennis does not appear beyond this segment.
- Despite being a more notable Variant, Dennis has no specially designed or customized character model.
- In the game files, Dennis' name is spelled as "Denis".
- It can be speculated that the stuttering brother's personality is Dennis' original. This is due to the verbal abuse he seems to suffer from the other personalities, to which he seems to willfully ignore. The three alternate personalities also each have a key behavioral trait, a factor that's common in realistic MPD cases.