There are three "worlds" in this setting: Heaven, Hell and Midgard, Midgard being Earth and the entire Milkyway galaxy.

When a demon or an angel enters Midgard, they can't just walk there, as they need a body to be able to interact with it. If the body is destroyed, the demon is sent back to Hell with their memories intact.

Turnaround time (Tt) is the time it takes for a demon, immediately after their physical body is destroyed, to create a new one.

Tt varies from demon to demon, high-level demons like Zizel or Lime need hundreds of years, The Icon of John Romero needs a thousand years, "mediocre" ones like Marauder need weeks, however, there's a special class of demons, called Eternals.

Eternals aren't particularly tough or well-armed. Some have rocket launchers, others have shotguns, machine guns, and a handful possess mortars, however, they have virtual turnaround times as low as one millisecond, making them the ideal footsoldiers for invading Earth and holding position. Now, they accomplish these insanely low values by cheating the system. They have multiple bodies pre-made, albeit only one can be active (possessed) at any given time.

However, for the story, this poses a few problems. Of course, Eternals are numerous enough that simply having them active all at once will get you 10 000 units of unique demons to work with. But the main team of the story, the background dancers, have been fighting the same demons over and over again.

Sure, Doomslayer, Sammy and VEGA are leagues above them, so any improvement would go unseen, but the background dancers need each other to survive against the demon horde. This means that the Eternals should show signs of adapting to combat the humans' weapons and tactics, especially since they go up against the same five. It's not like there's anything better to do.

Yet their tactics and moves remain unchanged. They do have intelligence and are able to speak, though you sometimes wish they weren't.

I'm looking for a practical reason. Why do Eternals refuse to adapt to combating specifically humans when all they had to do was to take over that damn planet, CJ!

At the point of the invasion, Earth has modern-day technology.

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    $\begingroup$ Why do you think demons should have the ability to learn? Those Eternals might be already at the top of their ability. $\endgroup$
    – Alexander
    Apr 6, 2020 at 22:24
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    $\begingroup$ why they need to adapt other tactic? they never die and can spawn back quick, their long strategy seems more reliable and a sure way to make pyrrhic victory happen, it even shown that your human start to get wear down from encountering this eternal demons that keep spawning over and over. i can also imagine this eternal corpse pilling will either pushing their enemy out of space or creating an epidemic if the corpse still lay around in that world and can decay. $\endgroup$
    – Li Jun
    Apr 7, 2020 at 7:19
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    $\begingroup$ A lot of the answers seem to be misunderstanding how adaption and evolution works - it doesn't require the thing evolving (adapting) to be smart or even self aware, it just requires there to be differences -- variability, in other words -- and the ability to pass differences on to their spawn (which in this case is the rebirth mechanism). I think a good answer might address a lack of variability in the demons (which means there won't be winning vs losing strats), or that they are so behind the curve that any adaptions they do have would be worthless against such superior enemy. $\endgroup$
    – eps
    Apr 7, 2020 at 15:05
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    $\begingroup$ @eps You’re missing a crucial part there though. In evolution the losing strategies are removed and replaced by more copies of the good strategy. Here the bad strategies have just as much ‘reproductive’ ability as the good ones. And since it’s a one-in-one-out population there is no room for evolution to take place at all. $\endgroup$
    – Joe Bloggs
    Apr 7, 2020 at 15:35
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    $\begingroup$ Perhaps your demons can speak and solve problems but are extremely weak on innovation. It simply will not occur to these eternals to modify their tactics unless somebody suggests it to them. –– You better hope none of them reads Worldbuilding SE. $\endgroup$ Apr 8, 2020 at 1:38

16 Answers 16


Why would they? They're just here to punch the clock. Invading planets nine to five, then check out and relax. And you know what? If you get killed, you get a vacation. Of course, it must not be obvious that you got killed on purpose - so you just do the job you got, exactly according to spec, without ever thinking about anything new. The managers don't particularly care either, and any attempts at invention or innovation are generally frowned upon. You'll get there eventually anyway, and there's no rush - no matter the kill/death ratios, you keep coming back - they don't. After a few hundred thousand years, this has become the standard operating procedure, and everyone is perfectly happy to just do their part at the conveyor belt.

Let's just hope they don't discover agile.

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    $\begingroup$ What’s this ‘Sprint’ I keep hearing about? Oh.. running quickly from one safe place to another?? Paradigm shifting!!! $\endgroup$
    – Joe Bloggs
    Apr 7, 2020 at 9:06
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    $\begingroup$ This is the truest of hells. $\endgroup$
    – M i ech
    Apr 7, 2020 at 10:01
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    $\begingroup$ Great outside the box perspective! The individuals couldn't care less about the big invasion and are just doing their mind-numbing job. $\endgroup$
    – Falco
    Apr 7, 2020 at 10:27
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    $\begingroup$ Methinks these demons could use some pair pro- err, marauding, to fight more productively on the battlefield. Perhaps they should also enlist the services of a few Drum Masters to raise their army's morale. $\endgroup$
    – AleksandrH
    Apr 7, 2020 at 14:08
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    $\begingroup$ And now I'm just picturing the demons and demon-hunters meeting at the punch-clock at the end or start of their shift - "Morning, Sam", "Morning, Raphael"... $\endgroup$ Apr 7, 2020 at 16:52

They do not know what the tactics were

Combat is a horribly confusing environment to be in. No one has the full picture of exactly what happened afterwards - recollections of individuals are contradictory and have been shown to be incorrect when compared to film evidence. It is only in modern FPS video games that kill-cam views show you how you "died".

This means that determining why a battle had a particular outcome requires detailed analysis from documentary evidence and all the eyewitness accounts that can be gathered. If the "Eternals" are reloaded into another body the instant that they are killed, all they have is their own limited, possibly unreliable viewpoint of their death. For example, a 155mm artillery shell landed among a group of Eternals and blew them to pieces - their only memories will be that they were at such-and-such location and then they were dead. (Soldiers who have survived being "blown up" never have clear memories of the event.) Another example would be that one "good guy" distracted an Eternal while another shot them from behind - the Eternal's only memory will be that they observed something that they may realise in retrospect was a distraction. However, if an Eternal is almost instantly being loaded into a new body with a mission to get back into the fight ASAP then even that limited reflection may be impossible.

The only way that the Eternals possibly could learn from their mistakes would be if they took extensive time out after each battle to recount what they each observed and have a skilled tactician add all the information together, which will make their "Tt" measured in days or weeks, not milliseconds. Without such a process the Eternals will be lucky to learn anything.

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    $\begingroup$ This is exactly it. There's no "killcam" when you die, where you get to watch the last 10 seconds from your killer's perspective to analyze exactly how it happened and why. One second you're shooting at some attackers, and the next you've taken a bullet through the head without realizing it. $\endgroup$
    – scohe001
    Apr 7, 2020 at 13:12
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    $\begingroup$ Learning how you died from video games without a killcam takes longer, but after 100 or so deaths, you still learn. $\endgroup$
    – Nosajimiki
    Apr 7, 2020 at 13:15
  • $\begingroup$ Except dying in real life is nothing like dying in a video game. Some of the times you have no idea what happened, and those are the important ones because it'll probably be from a special tactic (stealth kill, nuclear bomb, sniper, etc). $\endgroup$
    – Nelson
    Apr 7, 2020 at 16:40
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    $\begingroup$ Also, the OP says that they return with their memories, but does that mean every single memory right up until the very last moment? Even the loss of the last 15 or 30 seconds at the very end (due to shock/trauma/etc?) would likely make it almost impossible to figure out exactly what happened that got you killed in an awful lot of cases. Or perhaps remembering the very last moments is possible, but difficult/painful, so they generally avoid it because they've got no real motivation to put themselves through that anyway.. $\endgroup$
    – Foogod
    Apr 7, 2020 at 18:27
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    $\begingroup$ Seems a bit tenuous to me. Some of the kills might be uncertain amidst the fog of war but many won't. Given infinite respawns the demons should learn eventually. $\endgroup$ Apr 8, 2020 at 7:09

Because they're winning

Demons want to corrupt. They want to take good things and twist them. Humans, wrongly, believe that the demons are trying to conquer Midgaard, but that's not their aim. They want to keep the people of Midgaard in a state of fear, they want them to prioritise war and fighting over creation, art, and being good to one another. They want towns to cower behind walls instead of being wide open and airy. They want the heroes of the people to be warriors and killers, instead of artists and poets.

By keeping Midgaard in a constant state of war, they're achieving their aims. Altering their tactics so that actually won would end the war and defeat their real goals.

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    $\begingroup$ That is devious. I like it. $\endgroup$
    – Joe Bloggs
    Apr 7, 2020 at 18:55
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    $\begingroup$ Oceania was at war with Eastasia: Oceania had always been at war with Eastasia. $\endgroup$
    – kungphu
    Apr 8, 2020 at 1:17

Demons are immortal. As such, they’ve had a long time to get used to doing things a certain way. Their tactics are aeons old, even if their bodies aren’t, and because they have such a quick turnaround the tactic of ‘mob them’ has been ingrained over millennia of warfare. It’s not that they don’t see what’s killing them, they just can’t wrap their heads around why they should change the tactics of the ages.

Just like your older relatives might shake their heads and tut when asked if they can use a computer, even though using one has clear advantages, the Eternal demons shake their heads and tut when asked about any tactic more advanced than ‘run-n-gun’. It was good enough back in the Abyssal campaign of The Year Of The Blooded Goat, so it’s good enough now, thank you very much.

And the younger demons, who haven’t got the experience to turn themselves around as quickly but are far more flexible in their modes of thought, just put their heads in their multitudinous hands and cry whenever they’re asked to ‘just pop over and help with a human problem I’m having’.


Because they're very stupid

Yes, it's a very cliche answer and it's not particularly creative, but there's nothing wrong with using it as a concept, especially when it comes to the 'background noise', as you might say. Power generally has to come with a price and a restriction. It makes sense that there's a price to pay in order to resurrect instantly with all memories intact, and that price is going to negate the advantage somewhat - and here the price is stupidity. These demons are just too stupid to learn from their previous mistakes. They don't have anything resembling human intelligence. They're just that stupid.


Speed vs Accuracy

The quick transfer comes with a downside as well - no error checking, no CRC - the transfer is quick and dirty and 'corrupts' the long term memory each time its done and loses the data in 'RAM' or the short term memory when the demon 'dies'

High level demons on the other hand have a very involved and detailed process to transfer their memories involving a lot of error checking, redundancies, backups (of backups of..). The process is therefore slow (and expensive), but also extremely accurate.

  • $\begingroup$ Welcome to the site and nice first answer! Your idea has some synergy with mine - possibly the high level demons both have the error checking etc and conduct a detailed after action report to avoid making the same fatal mistakes next time. $\endgroup$ Apr 7, 2020 at 8:35

It is the downside of premaking your bodies.

They have the experience and knowledge of the demon, when they created them, rather than the experience and knowledge of the demon when it transfers into them.

The Demons might* retain some short term memories when forced to shift from one body to another premade one, but they don't easily get transferred into long term memory, and as a result generally get forgotten, over a number of hours to a few days.

*Some weaker eternals might not even be able to do this, which would give a moment after they come back when they don't know what is going on.


They have multiple bodies pre-made, albeit only one can be active (possessed) at any given time.

Those bodies were pre-made long ago. They aren't (yet) making more. In the military getting things turned around and adapting takes a while, and they do use the resources they have already. Numbers have likely worked in the past. They aren't going to waste resources on adapting grunts when those grunts already have 1,000 bodies each ready and waiting to go.

For the higher-level ones with a longer Tt, well, they have a number of bodies as well, and it would take them even longer to adapt something new.

The short turn-around time means that they don't actually have time to give any kind of report on tatics and what killed them. How can they possibly adapt when given a millisecond to respawn? Those bodies are already pre-made. If they gave a full report or had the ability to make a full report between getting killed and coming back in, they might well not be able to overwhelm the enemy. So your grunts do not have the option, and the ones with the longer times (bosses and such) might have that as a way to upgrade and lower-level guys just don't.

The more diesel the body, the longer it takes to "connect" the host to the new body. So while they might have their full memories intact, during the connection process they can't DO anything. This might mean that they spend the entire 2 weeks or 100 years simply reconnecting to the new body.

Adaptation means that things have to change. If the tactics they have developed over time have always worked for them, eventually, why change them? They don't have a full picture of the war, just their own experiences--they know they'll be back and they only have to kill you once. They have centuries, millennia. You'll be dead soon enough.

They have it programmed within them. For the body-swapping to work, though they might recall you, all these tactics come pre-programmed in every solider. This is the only way they are able to have such evil minions work together and only FOR the cause. Giving their soldiers more free-will is a disadvantage for the over-lords in the long run, but in the short-term, the heroes can use it to their advantage. And because they don't think in terms of human life-spans, the over-lords see no reason to allow it, which would also allow the demons to, one day, exercise that will to overtake them.


They don't really want to win (quickly) because in the current status quo they are important to their masters. But once they overrun the Earth and win, then higher level daemons will follow and take over making them totally insignificant again. Putting that in the light of being immortal, a few centuries is nothing for them, so they just stick to the current situation for now.


It sounds like you haven't played very many online video games, because if you have you would have met "that guy".

Nothing is his fault, every time he dies its the lag, or his team mates or because the game was designed by idiots, but the last possibility he would ever consider is that his decisions or actions might have fault in them.

He's somewhat immature, narcissistic and believes he knows everything. You will see him barreling down the same pathways, doing the same tactics, dying to the same person and throwing out the same excuse every minute or so.

Your demons aren't dumb or under armed or even un-evolved, they just have personality disorders, which, sounds like a demon to me!


Why do some people serially engage in abusive relationships? I doubt there are therapists for demons, but my layman's take is that even though they know it's a bad idea they

  • are blind to the pattern
  • think it'll be different this time
  • deep down think they don't deserve better
  • ...

They always did it this way and it always worked out fine

... before now.

It's not that they are dumb or something like that. It's that it always worked. They waged wars before and they won them. They crushed entire worlds using this strategy. They believe in it.

Maybe some of them are not so fond of this strategy. A good antagonist might step out of line and adapt, while his peers want him to go back to the "winning strategy". Unless they have been losing for decades, what's a couple battles or a couple years to immortals? It's a drop in the ocean of time. The ones who "adapt" are the weirdo and in the past it has always been a pitiful waste of time.



They could be fairly intelligent, approach sites in a semi-tactical manner, etc., but when they actually see the humans they lose their mind and just want to spill some blood. This simplicity could be the reason they never got up on the demonic corporate ladder. :)


When you play a computer game, like a FPS, you get better over time. But after a while... you don't get MUCH better. You don't very often figure out a whole new tactic to change the way it all works.

At least you have your muscle memory that improves, rapidly at first and then slower over time. Good thing you're not changing your body like these demons every time you died, or you'd lose that advantage, too.

So, they got OK at this level of the game. Not brilliant, and not enough to figure out a way to skip the level, but good enough to sometimes kill a player.

If you regularly play a FPS against your friends, you'll find this to be the norm: your relative ability against them doesn't change much after the first few games.


They are already at the end of possible tactics

It's been few hundreds years since we developed armour to protect ourselfs in combat. And we also developed better weapons to counter that armour.
Then why we have helmets to protect use from headshots by we don't have nice headgears with that? I think, when faced with possibility of getting shot in the face, I would prefer to wear a dog face helmet than a balaclava.

It might be due to the price and time needed to make armour versus just spawn another human sleeve.

Also Eternals might not have a lot to say in what body they land in. Grunt, Burnt or Flunkd. So they amass experience in much slowe rate than the 5 they're facing. They adapt, but background fighters are just few steps ahead. You cannot downplay the body-mind connection. Eternals might learn how fast the fingers on Grunt react, how fast the trigger falls, how long the bullet would travel distance beetwen them and target. They might not know that it's useless to pull that trigger in the first place as all those times combined are longer than just jumpin to enemy, grabbing their skull and crush.

After a while you discover you cannot push tactics further. You either try to bury them in corpses and have 101 soldiers against their 100 bullets or you realise there are not much variations of "jumping them from around the corner".


May I suggest a plot twist? Maybe their turnaround time only seems long to the humans and in fact is short (or short to the demons). In other words, it's not that they aren't capable of adapting, it's that they don't choose to!

But why would the Eternals do this? The way I see it, there are three possibilities:

  1. Sinister Scheme-The Eternals are trying to lull the humans into complacency; when facing a clever, adaptive opponent any smart fighter keeps on their toes and becomes unpredictable. If the demons never seem to adapt, why would anyone develop new tactics to beat them? Problem is, the demons are simply planning to get the humans where their tactics are always predictable so that then they can do a sudden turnaround and attack with perfect knowledge of the human's tactics, the weaknesses of said tactics, and how to exploit them.

  2. Nonlethal Intentions-The Eternals want to capture, not kill, the demon slayers, and that includes the five background dancers. Their superiors have realized that if they create new Eternals by capturing and converting the demon slayers, they'll get Gen 2 Eternals-more cunning, adaptive, versatile, and all-out deadly than regular Eternals.

  3. They're sizing them up-A variation of Sinister Scheme; perhaps the Eternals are merely playing dumb while they size up the competition. Once they've collected enough information, then they go in and use everything they've learned against the supposedly strategical superior humans. Alternatively, this could be a case of the Love at First Punch trope-demons don't date like normal people, they spar instead to see if someone is a worthy partner. This could be one of the weaknesses of the Eternal system: they're essentially demons in human form, so they can (and will) be attracted to anyone who can face or better yet, beat them. If this idea interests you, please see this link: Love At First Punch

Anyway, hopes this helps!


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