Ichor

They look a bit more like paneling than doors.

Oh yeah. I'll add those.

In order to use any of the weapons, you have to: 1. type "PICK UP X" (X = the specific weapon) to pick up the weapon. Otherwise, you will pass over it. 2. type "PICK UP Y" (Y = the specific ammo). 3. type "PICK UP Z" (Z = the specific item or powerup). 4. type "SELECT X" to switch to your weapon. 5. type "FIRE X" for each time you want to fire a shot from your weapon, even the chaingun and plasma gun. 6. for any mods that include weapon reloading, type "LOAD Y INTO X". Also to open doors, type "OPEN DOOR", but only if it's a normal door. If it's a secret door, type "OPEN SECRET DOOR". One won't work with the other. And for switches, type "USE SWITCH TO W (W = the specific action)". Type in the wrong action and nothing happens.

Even if you don't have the BFG, its size means you could hide behind a corner and you could still shoot it (for best results, use a hitscan weapon). It needs to be smaller, or better yet, the vulnerable area should be smaller, like only the brain portion could be hurt.

Doom on a Virtual Boy

Maybe it's similar to Lemmings. Your goal would be to help the demons reach doomguy and prevent them from falling off, getting crushed, etc.

Make it a multi-tier boss. 1. Same as the spider mastermind. 2. The legs fall off, but the center remains. A few seconds later, tank treads emerge and it's somewhat faster. This part will shoot mancubus-like fireballs. 3. The center falls apart, but the brain remains. Then it rises up and starts flying around on its jet propelled platform. This part will psychokinetically cause rocks to materialize around the brain and then launch them at you (+/- 5 degrees or so) in a rapid fire fashion. Rarely, it will fire a BFG shot, but it will take a second or two to charge up to give the player time to prepare for it.

When I think of nightmare fuel for Doom, I think of causing paranoia. Some things that can cause a lot of paranoia and make you uneasy and overly cautious for a while: A cyberdemon or spider mastermind overlooking much of a map, and you without enough firepower to deal with it immediately. Opening a door to find a couple of arch-viles...only to have them instantly teleport away from you to an unknown part of the map. Random jump scare/instapop anything in an area you've been in a few times before. A maze-like area with monster only teleport lines that send monsters to a nearby spot (similar to that baron map 29). You're in a room and a bunch of cacodemons descend through an open skylight while you're distracted by some other enemies.

I'm coocoo for Caco Puffs.

Here's another good idea:

cacodemons.com doesn't appear to be taken, and the name "cacodemon" isn't copyrighted (since the term itself means evil demon or spirit).