Cool Doom Glitch [Barrels]

Hello there. I was just playing my Ultimate Doom map base.wad in prboom+ v2.5.06 and I shot a barrel with the shotgun which killed a couple of Imps out of a group, and then one of the surviving Imps turned on another Imp and started scratching him. But I shot the barrel not the other Imp. This thread might belong in Source Ports but I am just wondering what happened. Normally the other Imp would have damaged the first Imp and caused retaliation, but not in this case.

What happened?

This sounds like "normal" behaviour, if one of the imps had first caused some damage to the barrel. (What matters from a retailation viewpoint is what first caused damage, not what finished the thing off.)

If you had been recording, then I'm pretty sure the demo would have played back the same way with whatever exe you had been asking it to emulate. A major compatibility bug in something as basic as this is most unlikely, and would have been noticed by now. What complevel were you using?

This happened to me in PSX Doom once. I was on Map 2 (Plant) and I shot the barrel in the room with the 3 Imps on ledges. When I shot the barrel, one of the imps on the ground started attacking one of the Imps on the ledge, and ended up killing him by scratching him from the ground. The biggest WTF kill moment I've ever had playing Doom.

After a bit of digging around...

This issue was discussed here.

Here's another discussion on the topic of infighting, where Quasar also explains the pain threshold, that is responsible for making the imp angry at the other imp instead of the player character.

Happened to me in UAC Ultra a while back, when one Hell Knight turned on another.

No complevel setting, I was just playing for the sake of it. I did not see the Imp hurt the barrel before I shot it, but that must have been it. Pretty cool though, I killed the Imps before they finished their scratching match.

Wish I had a screenshot.

Espi actually made a map around this idea:

http://www.doomworld.com/idgames/index.php?id=10749

I alway enjoy messing around with this glitch. I almost always get to the two Hell Knights on Scythe Map06 to fight in the last room. It really helps to have those two distracted.

Do the two same species monsters actually kill each other in some source ports and not in others? I remember one time I got these two cacodemons to fight each other with fast monsters on but they never died. They kept hurling fireballs for like 20 minutes while I continued to the other half of the map, then I came back to see them gnawning each other's faces off (it was pretty romantic) but neither of them would die until i killed them off. I forget what port I was using though.

The original Vanilla behaviour is:

Monsters remain immune to projectiles fired by others of the same species, even when they are infighting with their own species.

However, they can hurt each other with melee attacks.

Hence, two Aracnotron's are never going to kill each other, but two Hell Knights will if they can get close to each other

I assume the Pain Elemental is immune to in-fighting too, because of the nature of how it attacks?

Should another monster hit it with an attack, it'd retaliate with Lost Souls, causing the lost souls to be the target of retaliation. Correct?

Yeah, and what's more is because lost souls are retarded, once they stop flying (whether or not they hit the intended target), they'll turn and go after Doomguy again. So Pain Elementals will keep spawning, and it'll keep spawning... In the end, it won't do very much damage.

40oz said:

Do the two same species monsters actually kill each other in some source ports and not in others? I remember one time I got these two cacodemons to fight each other with fast monsters on but they never died. They kept hurling fireballs for like 20 minutes while I continued to the other half of the map, then I came back to see them gnawning each other's faces off (it was pretty romantic) but neither of them would die until i killed them off. I forget what port I was using though.

Cacos can certainly fight to the death, as their bite attack will damage each other. Here's an example demo:
http://classicdoom.com/odddemos.htm#cacofite
Fast monsters will make them more likely to use their fireball attack if they are not right next to each other, but from what you say they were biting each other when you came back to them. The bite is powerful, so one of them ought to have died fairly quickly once that started happening.

BTW, here's another related thread:
http://www.doomworld.com/vb/showthread.php?threadid=44000

Snakes said:

Espi actually made a map around this idea.

myk said:

Here's another discussion on the topic of infighting, where Quasar also explains the pain threshold, that is responsible for making the imp angry at the other imp instead of the player character.

There's some neat stuff about the archvile's attack in that thread too that I never knew before. I already knew that the archvile's attack had two parts - the 20 direct damage and the ~70 splash damage - but I didn't know that you could nullify the splash damage part of the attack by positioning yourself so that the explosion's "epicenter" is in a place from which explosions can't hurt you (eg. outside of the level, in "the void"). I was testing this just now, and you can consistently take only 20 damage from an archvile attack if you can "force" the explosion outside of the level, or onto a ledge above you. While testing, I think I also proved some conventional wisdom wrong. The archvile attack's "flames" aren't actually the source of the explosion. The explosion comes from a point very close to the player, but this point is always between the player and the archvile. If an archvile attacks you, and you turn away from it and rub your face on a wall, "forcing" the flames out of the level, you'll still take both direct and splash damage. However, if there's a raised sector between you and the attacking archvile, and you're pressed immediately against it, and if the height of this sector is just right so that the archvile can still see you but explosions up on the raised sector won't affect you, then you'll only take 20 damage from the archie's attack. More evidence that the explosion always originates between the player and the archvile is that, no matter which way you're facing at the time, an archvile's attack will push you away from the archvile.

I'd love to make use of this splash-damage-avoidance trick when playing, but level geography has to be absolutely perfect for you to use it. I was testing this on "Gotcha," in the Cybie & Spidey arena, and found that, as the archie runs around on the ledge bordering the room, you can avoid the splash damage of its attacks by keeping the right stair, in the flight of stairs that leads to the boss platforms, between you and it. Hide behind too low a stair, and you get hit by both parts of the attack. Hide behind a high stair, and the archie's LOS is blocked entirely (which I suppose isn't such a bad thing, thinking tactically).

Yeah, it's nice in some set-piece situation that you have planned in advance in a level you know (and have looked at in an editor), but hard to use on spec in some random situation.

One demo where I used it deliberately can be found in this post. Generally, the most useful situation for this idea is where you don't want the archie's blast to knock you backwards so that you can jump up onto a platform. Of course, the health can be useful too, as in this case.