Anyone else notice this?

On E1M6 of the original Doom, there is a door on the north-west side of the map that is initially opened by a switch that rests in a tower in the northernmost area of the map. I've occasionally seen this, but it seems that after you enter the area beyond that locked door, the door will random open after it has closed, even if you aren't moving.

So I recently used the second mode of the IDDT cheat to see if there was some kind of object that was opening that door, and sure enough it looks like there is some kind of invisible, harmless monster roaming around that area that will attempt to follow the player like an imp, opening and closing any door it encounters.

Has anybody else noticed this? I looked on the Doom wiki to see if this had already been cataloged as a bug, but I didn't see it listed anywhere. Note that I was playing the Ultimate Doom version 1.9 iwad on PrBoom v2.5.0.

The Invisi-Imp strikes... Really weird though. Have you tried this on other ports? Or could just be a glitch with PrBoom?

I just tried it again and I didn't notice anything unusual. Maybe it was just a really weird one-time glitch.

I did more looking on the Doom Wiki and found an unnamed invisible enemy that only appears in Hacx, but I'm certain this happened in Doom.

Is this invisible monster actually present if you check the map with a level editor, or is it some phantom artifact that the Doom engine or your source port is creating out of thin air?

I remember this happening when I used doom legacy a lot and played the "REAL" TC (with levels set in the jungle). There were some sound things that wouldn't show up on the automap but I knew were following me around (I could see the splashes as they hit the water thanks to legacy's splashing effects.)

To this day it bothers me a little bit.

REAL TC? What's that?

Maybe this?
http://www.doomworld.com/idgames/index.php?id=9274

Sounds scary.

If this is what I think it is (sector 37) then it is not random at all. Walking over linedef #868 (which the player usually does when heading towards the exit) activates line special #76 which causes the door to close for 30 seconds then open again (the player is usually far away by the time it reopens.)

I don't know about the invisible monster, but even if a monster was present it would not be able to open that door.

Then what the hell was following him?

Sounds like foaming processes are at work.

Clonehunter said:

Then what the hell was following him?

A monster. But it didn't open the door (the line types involved are not able to be activated by monsters. Also linedef #857 blocks monsters so the monster cannot cross the threshold into/out of the nukage pool.)

A monster could have been hiding in one of the other rooms in the area (e.g the dead-end in sector 22, if the monster was chasing the player towards the exit room) and eventually (with random movement) it would find its way down the stairs.

As for being invisible? There is a spectre in that area. It is easily distracted by in-fughting so it is easy to miss it and it can sneak up on you after you have killed the ambushing monsters near the exit and the doors have reopened.

Finnw's explanation most likely explains this last occurrence, although I'm probably thinking of two occasions at once because I remember experiencing the same things Csonicgo describes as well.

Oh well. Thanks for clearing that up.