The Nightmare Room Puzzle is a puzzle/loop in Resident Evil: Desolation. It is found in the C (co-op) campaign between Claire Redfield and Jill Valentine.
Act One
Jill enters the Nightmare Room, noting a few gurneys carrying body bags in front of her when a hallucinogenic gas suddenly pours through the room. Jill gets sucked into a seemingly endless dark loop with only her flashlight to guide her. She passes by insects on the walls and mutilated corpses hanging inside of booby traps in grim fashion. Along the way, she hears the sound of something feasting. Slowly navigating, Jill approaches the creature and is met with the all-too familiar sight of a zombie turning to face her after feeding into a corpse, revealing itself to be none other than Dark Alex, human blood smeared all over her new-and-improved, horrifying face. Turning around, she encounters more zombies head-on, disappearing as she changes course in a loop.
Bypassing the terrifying zombie apparitions creeping around every corner, Jill then runs into a trap door opening up. A group of scientists emerge from the sliding door, but they soon turn into a frenzied panic as they're slowly devoured by an Uroboros blob, their faces literally being peeled off of their face as a black fluid starts coursing through their skull and veins to a set of constantly flickering lights. The lights stop flickering as they're devoured whole, however, a set of sporadic guide lights shows the blob slowly creeping around Jill on the walls as she continues through the loop.
Mutant fetuses then begin to fall from the ceiling, hanging from mutilated umbilical cords. An all-too familiar girl's voice starts singing a haunting recital of "Rockabye Baby" which is interrupted as a pack of eviscerated mutant heads flings in Jill's face attached to slimy dark matter. An Uroboros monster then frantically crawls away in a frenzied fashion as it races down the hall.
Once again transforming itself, Jill now finds herself in a dark hallway surrounded in red haze, eventually coming across a girl standing in the hall on the other side as it enters a windy hall loop. The girl vanishes, but Jill continues to navigate the hall, eventually coming across the disturbing site of Mannekills peering out in front of her. She is caught by surprise by the sudden appearance of Dark Alex, who causes Jill to stumble off her feet as she magically pops up in front of her. Facing the wall to her left, she sees a figure levitating off the ground. Jill follows this figure's every footsteps, catching only mere traces of bare flesh via her flashlight along the way. While pursing the figure, Jill's flashlight catches the disturbing site of mutant legs and mandibles flinging as she walks by apparitions of an Incubo and Manta. The figure then reveals itself in full, exposing her bare breasts and horrific demonic face as "Evelyn" passes Jill, a black bush covering her genitals.
Nonetheless continuing down the hall, the horrific sights continue as barely-visible corpses begin to rise off the ground. Haunted by glistening moans but no visible body, Jill is once again caught by surprise as a live Condemned begins to pull itself out of a sawblade to attack her. Jill disposes of the creature, but runs into yet more zombie apparitions swarming her around every corner as she keeps changing course. Jill keeps moving forward while evading the zombies, but is knocked off guard by an unseen force. Slowly making it back to her feet, the figure reveals himself to be none other than Albert Wesker, who sics a pack of dark-bodied Phantasms after her while swarms of vampire bats surround them from all angles in a cyclone wall.
"If you can't beat us... JOIN US!"-Albert Wesker
Jill narrowly escapes the Phantasms with her life, finally making her way out of the neverending loop as she reaches the end of the bat swarm.
Act Two
Making her way back into the main lab, Jill. However, the mind games continue as a gas sweeps through the facility following another power outage at the hands of Dark Alex.
"Had enough? I'M JUST GETTING STARTED!"-Dark Alex
Jill approaches the three bodybags laying on gurneys in front of her. Wary of surprises, Jill slowly opens them up, finding a corpse gutted to the bone in grim fashion in the first body bag before discovering a demonic zombie-like Phantasm turning to her side, chanting "save us" in the second. Disturbed, Jill begins to slowly open the third, only to find it empty. However, a nearby disturbance catches her attention.
Jill slowly proceeds down the hall to investigate, finding a vile laying on a cabinet where a lifeless nurse hangs face down upon. However, the zombie nurse suddenly springs to life and tries attacking Jill as she attempts to turn her around. Jill evades the nurse while grabbing the Ven Muse vile. However, she stumbles off her feet as something trips her up. The lights begin to flicker, revealing Cadavra suddenly emerging from the previously-empty third bag. Jill frantically gets back to her feet and runs for her life, desperately trying to find an escape route. After a frantic escapade, Jill finds and hurriedly opens a locked side door with her lock pick, opening just in time to slam the door shut on the horrific live corpse. Jill barricades herself as it tries to break through and slowly approaches the door laying at the end of the hall. However, Jill is once again caught off guard as a burning zombie emerges from the nearby furnace.
Jill kills the zombie, but is met with a suddenly flickering light behind her. Jill slowly approaches the window with her flashlight-mounted gun cocked and is met with the disturbing sight of Alex's horrific face appearing in the window, bearing a chilling message written in blood before vanishing. Finding her next clue, Jill backtracks down the hall and turns the corner. Noting the door is welded shut by wiring, Jill starts making her way through a series of maze-like set of rooms in a barbaric puzzle, danger awaiting her around every corner. Jill eventually finds a tank with a wiring attached and pours the looted agent into the container, snapping the wire as it begins to dispense the compound.
Using a nearby ventilation system to backtrack through the barricaded room, Jill proceeds through the unlocked door into a tentacle-filled hallway. Jill navigates down a series of L-shaped hallways with tentacles swaying through the air ducts, but takes notice as a creature is vaguely seen moving through the crevices when the hallways suddenly begin to clear.
After reaching the end of the trail, a large tentacled blob creature suddenly emerges from a grating in the wall and is continually growing larger as it's injected with the Ven Muse agent Jill obtained to complete her puzzle. Using her Genesis scanner, Jill finds a proximity mine and aligns it with the location of the furnace on the other end of the hall, obliterating Deathala as it tries to devour her. However, Jill notices swarms of aggregates splitting from its destroyed remains as she sees nestling in the rubble beneath her. She finds herself faced with yet another horrifying obstacle as burning Condemned emerge from the ground after splitting and merging together from the destroyed creature, with black dye oozing from their burning amalgamated flesh. Jill navigates the premise, avoiding both flame and critter alike to find a lever.
Unlocking the door in front of her via crane, Jill is met with a pack of Incubo awaiting her on the other side of the hall. However, they tumble and start puking bugs as Jill finds herself surrounded by swarms of leeches on all sides. Jill continues down the leech-filled tunnel and is met with several horrific leech-infested apparitions, including one that grabs her leg and moves in to bite her before vanishing. The worst was yet to come, however, as Dark Alex begins to emerge from the ceiling. Dancing and hanging in front of Jill in a hypnotic trance, she follows her every move down the tunnel, taunting Jill every step of the way in an attempt to frighten her.
"Have you learned to fear me?"-Dark Alex
Act Three
Dark Alex eventually vanishes as the leech swarm loop comes to a halt. Now back in the unaltered hallway, Jill continues her search when a Necromongul bursts out of the nearby vent after turning the corner. Jill blasts the nearby fire extinguisher to temporarily blind the creature as she attempts to escape through an increasingly-narrow crawl space in front of her, narrowly escaping being eaten while it attempts to squeeze through.
Making her way back into the main quarters of the room, Jill is treated to a vat of blood that begins to rise off the ground, forming a blood wall around Jill throughout the remainder of the room. Jill searches the back lot, using her Genesis Scanner as a guiding tool. Using cover and her scans, she narrowly evades all 3 of Wesker, Cadavra and Baroness to find the Daystar hologram device, which she uses to find the toxin-deactivating lever after placing it on the digital scanner.