Although Collin Phipps says it's extremely rare, it happened to me once, on that TVR/Revolution map where you are inside a giant worm. At first I was like, what the fuck, and I thought the author just experimented with the Doom mechanics and it was intentionally done to make the strange map even stranger. However, after reloading my saved game everything was fine again.
Besides that, I happen to see ghost monsters from time to time, usually in Alien Vendetta. Don't really know why, maybe because the maps are well-detailed and monster-laden at the same time.
Yes but I turned its emulation off because while it's amusing, it ruins speedruns.
The best way to trigger it that I know is to play NUTS.wad on Nightmare, happens all the time. But sometimes it happens even in extremely simple situations, check out the infamous BLACKTWR uv-speed demo for example.
I made the supershotgun have millions of ammo and fire 1 shot per tic with dehacked. Then I loaded Go 2 It, ran around the level activating all the traps and started shooting. Pretty soon no one could hit anything anymore.
A long time ago I tried to deliberately cause it on MAP30. I read at that time that the bug is caused by a memory overflow, so I thought if I let too many monsters spawn in, the bug will occur (at that time I didn't know how to run PWADs in original engine, I only could launch Doom 2 in DOSBox). After (*only*) almost an hour (maybe only half an hour), I impatiently gave up.
EDIT: Now when I read your notes about intercepts, maybe I will repeat my experiment on a more suitable map.
Yeah I remember the first time that happened. I was playing one of my own WADs and in the middle of a fight everything... changed. Really weird experience. Took me a while to realize that I was a ghost myself... kinda my own personal Sixth Sense moment :P
I've encountered ghost monsters quite a few times, both in levels where they are intended to appear (like that one late level in Doom Jr... yeah) and in normal levels too. The all-ghosts bug is something I've never personally encountered, though this is partially due to the fact that I've been playing ZDoom/derivative source ports for probably over 10 years now.
Hmm, I can kill HKs with splash damage using automap and double IDDT to aim but I don't see any way to kill other monsters. I'm intrigued.
edit: and I don't understand how that KILL room could help, nothing special happens there...
This is so weird. From what I thought about all ghost bug, this (a place where the bug loses its effect) shouldn't have been even possible. And you say you don't know how you did it? Did you at least intend to make such sector when starting your map? Anyone knows something about that?
I encountered it while I was testing one of my levels. Think it was caused by too many linedefs I used to make a complex symbol on the floor.
Does anyone know if there's any plans to fix this bug for good in future versions of Zdoom/GZDoom/Zandronum? (or be made into a toggle or something for the people who like the bug) I remember it was pretty annoying having that happen in my game when I wasn't intending it to. This was from a level I scrapped a year ago before my break from modding and I haven't made any insane amount of linedefs since.