WIP The Part where Everything went to Hell
I'm going to finish Traps first to get an idea on making better traps, rooms, etc. before I start on this bigger project.
turret 1: I think I saw anybody more to kill.
turret 2: That will be fun.
turret 1: Bloods is sweet.
etc...
Flaming is easy and cool, you can use new theory things like "dark things" and "light things" where dark hurts and light destroys light, for example a dark door, you cant touch it and you need to use a mirror with lights to change it to light, etc...
Broken dolls is a good idea to make a horror theme. And more, you need surprises, inexplicable things and traps, traps more sadic than glaDOS and wheatley. I think is a good idea but you will have muuuuch work 
good luck.
As the above poster mentioned, surprises are good, too. Hidden doors opening unexpectedly, complete with sound effect to startle the player. Lots of corridors where you can't see what's around the bend.
And don't forget all the decals of crumbling and water damaged walls. I think concrete walls would be good for this map.
Oh, and I'd use the rusted cube skins for this. Nothing should be bright or clean looking.
Edit: To clarify on a few things, the main character/Chell will still be in Aperture Science, however this is more of a "What if" situation. What if GLaDOS was more sadistic? What if the traps were more threatening? Anyone that's heard of the "What if...?" Comics will know what I'm talking about. I'm just trying to make everything scary, but to keep it Portal 2 style, no dolls and stuff like that.
One other idea I forgot to mention is GLaDOS peeking out of a wall and then the wall shuts itself. Maybe bring back the "She's watching you" painting.
Also having a random panel popout/crush something close to the player might also scare the crap out of the player.
And another thing that you could use, most of the panel arms have 3 skins, one displaying the famous cyan colours, but also a red one and a dark/off one. you can hide things from the player with a black skin, and then turn the skin to red when everything starts to move. 
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VVVVVVVVVVVVV T
I can honestly say that the single moment in Portal 2 that freaked me out the most was when GLaDOS began humming "The Bear Climbed Over the Mountain". Almost genuinely disturbing, and I'm not even sure why.
be sure to add some red omnious light to the room behind the wall/floor/ceiling.
Also you could do a "upside down" room where everything that should be on the floor is on the ceiling, along with a nice and complicated puzzle to solve 
another thing you could do is to let panels assume a chaotic position, like when glados got detatched and before wheatly got attached. (or you could just copy that very core room)
And dont forget to put "did you know that people with a guilty concio.. MEEEEEEEEEEEEEEEP... oh did i startle you?" to the list of things she says
Another good idea, used blood splatter texture to warn where not to go.
WinstonSmith wrote:
Just putting this in here:I can honestly say that the single moment in Portal 2 that freaked me out the most was when GLaDOS began humming "The Bear Climbed Over the Mountain". Almost genuinely disturbing, and I'm not even sure why.
That creeped me out too. I was like why is she humming? ROBOTS CANT HUM!
Then I realised that there was that secret with the singing turrets there. Singing turrets are kinda cute though... Just contradicting myself here.
WinstonSmith wrote:
Just putting this in here:I can honestly say that the single moment in Portal 2 that freaked me out the most was when GLaDOS began humming "The Bear Climbed Over the Mountain". Almost genuinely disturbing, and I'm not even sure why.
Actually, she was humming "For he's a Jolly Good Fellow," (It also says so on subtitles) she was also going a bit slower while humming the "which no one can deny" part. 
I'm going to try to make GLaDOS more scarier than SHODAN. Now that's going to be a challenge.
Another idea, I'm going to make the Haunted Hall of Turrets. How would you guys feel if turrets appeared out of the blue?
MasterLagger wrote:
WinstonSmith wrote:Just putting this in here:
I can honestly say that the single moment in Portal 2 that freaked me out the most was when GLaDOS began humming "The Bear Climbed Over the Mountain". Almost genuinely disturbing, and I'm not even sure why.
Actually, she was humming "For he's a Jolly Good Fellow," (It also says so on subtitles) she was also going a bit slower while humming the "which no one can deny" part.
Ah. Same tune and I never use the subtitles, forgive me.
On that note, anyone else think it would be scarier/more ominous if the song was "The Bear Climbed Over the Mountain" than "For He's a Jolly Good Fellow"?
think about all the dead testsubjects.
what if all those testsubjects became zombies? O.O
DAWH95 wrote:
skeletons,many skeletons!think about all the dead testsubjects.
what if all those testsubjects became zombies? O.O
I would like to see your come up with the code to get the NPC's working.
But skeletons would be scary... WOOOOOOoooooOOOOooo
What if, instead of turrets appearing and disappearing, you see a zombified Chell appear then disappear.