Existential Threat Monster Help

[blackjack50]

I am looking for a type of monster that is an existential threat to the world. I know that there are things like Tarasques, but I’m not really looking for a massive monster. I’m more looking for something that is a threat to all life in a sense of mind control or maybe a swarm? Does anyone have suggestions for this?

[PhantomSoul]

Sounds like Illithids would be a go-to classic!

[blackjack50]

Sounds like Illithids would be a go-to classic!

Are they the same as mind falters?

[PhantomSoul]

Are they the same as mind falters?

Yeah, Illithids are Mind Flayers

[Millstone85]

A demonic invasion starts with secret cults, continues with swarms of hungry fiends, then sees the entire world slide into the planar black hole that is the Abyss.

[Trafalgar]

I like the idea of a young kid getting powers that grow and grow. The kid wants to do good but the powers corrupt him/her and ends up threatening the world.

Adam in "Good Omens"
Tetsuo in "Akira"

Stuff like that.

[MrStabby]

Slaadi? Shadows? Basically anything that can respawn quickly will be a big risk.

[Millstone85]

You could take inspiration from The Mist, Annihilation, and other stories where a region of the world becomes overrun by, or warped into, an alien ecosystem. Then the region begins to expand, progressively "xenoforming" the world of the PCs. I think it beats the typical swarm, because it feels like the world is not just being devoured, or conquered, but overwritten.

Demons can do that, except they make it difficult to convey the idea of an ecosystem. It is more like everything starts attacking everything else.

Illithids are awesome, but I wonder how much of the ecosystem they would really modify. They tend to focus on sapient creatures and their juicy brains, be it for consumption, conversion or experimentation.

There are old-edition monsters called the kaorti, elves who went on a flesh and mind warping trip to the Far Realm and back. Knowing no ecosystem that would properly sustain them, they are determined to invent one. So they modify the atmosphere and create all manners of pets. They can also turn humanoids into new kaorti, much as illithids do except (1) with a whole bunch of parasites instead of one, and (2) they are always recruiting.

[LudicSavant]

I am looking for a type of monster that is an existential threat to the world. I know that there are things like Tarasques, but I’m not really looking for a massive monster. I’m more looking for something that is a threat to all life in a sense of mind control or maybe a swarm? Does anyone have suggestions for this?

Monsters that replicate themselves with every victim.

[blackjack50]

You could take inspiration from The Mist, Annihilation, and other stories where a region of the world becomes overrun by, or warped into, an alien ecosystem. Then the region begins to expand, progressively "xenoforming" the world of the PCs. I think it beats the typical swarm, because it feels like the world is not just being devoured, or conquered, but overwritten.

Demons can do that, except they make it difficult to convey the idea of an ecosystem. It is more like everything starts attacking everything else.

Illithids are awesome, but I wonder how much of the ecosystem they would really modify. They tend to focus on sapient creatures and their juicy brains, be it for consumption, conversion or experimentation.

There are old-edition monsters called the kaorti, elves who went on a flesh and mind warping trip to the Far Realm and back. Knowing no ecosystem that would properly sustain them, they are determined to invent one. So they modify the atmosphere and create all manners of pets. They can also turn humanoids into new kaorti, much as illithids do except (1) with a whole bunch of parasites instead of one, and (2) they are always recruiting.

That is cool. Seems to work. My idea is that my “BBEG” is not actually the BBEG. He is just aware of the existential threat that is posed by something like these.

[Kuulvheysoon]

Ghouls, Shadows and Lycanthropes are classics.

If you've got access to books from earlier editions, Elder Evils will probably be of interest to you.

[Unoriginal]

Tomb of Annihilation has an interesting version of this idea:

An atropal, aka an undead divine foetus, is being fed the souls of everyone who dies in the Forgotten Realm via an artifact, in order to make it ascend into a full Death God and have it consume the world. As a side effect, all resurrection magic has stopped working, and people who have been brought back to life are slowly rotting.

You could have something similar: a creature is trying to become god of X, and as an effect the whole world is affected in an X-related way.

[Catullus64]

It could just be a really big thing that destroys by its very presence. A wolf that devours entire cities, a giant as tall as the sky, a phoenix whose every flight scorches the forests and boils the oceans. Something that feels more mythic and less sci-fi. A real classical end-times bringer. If you want something with stats, what about a quartet of Elder Elementals (Mordenkainen's Tome of Foes, Pages 198-201). They can be working in tandem to end the world, or (my preferred option) be fighting each other, and breaking the world with their titanic battles.

[Composer99]

a phoenix whose every flight scorches the forests and boils the oceans.

This makes me think of the kaiju Rodan.

Actually, Ghidorah or something inspired by it might work. In many of its appearances in Godzilla stories it is both alien and intent on destroying all life.

You could change that latter goal into (to borrow that excellent term upthread) xenoforming the world to refashion it into a worthy home. It could work the way legendary creatures affect the world around them, slowly spreading further and further from its lair.

[Dienekes]

You could take inspiration from The Mist, Annihilation, and other stories where a region of the world becomes overrun by, or warped into, an alien ecosystem. Then the region begins to expand, progressively "xenoforming" the world of the PCs. I think it beats the typical swarm, because it feels like the world is not just being devoured, or conquered, but overwritten.


I kinda did this with aboleths trying to bring parts of the world underwater. Humanity tried to create floating islands to survive. They also attempted to turn off divine magic and force the surviving humans into pacts, essentially forcing the only magic users into becoming a homemade water pact Warlock. Though now I’d probably just use Fathomless. It was pretty fun.

Anyway, aboleths I think work pretty well. But Mind Flayers are definitely a go to standard for this kind of thing.

[ff7hero]

There was a 3.5 Dungeon Magazine Adventure Path based on a Githyanki invasion of the Prime Material Plane. That might offer some inspiration if you can track it down.

[Millstone85]

That is cool. Seems to work. My idea is that my “BBEG” is not actually the BBEG. He is just aware of the existential threat that is posed by something like these.Then there is the question of what means they use that make them appear as the BBEG.

For instance, they may keep unsavory company:

One of the devils' schtick is to present themselves as the lesser/necessary evil, keeping the Abyss and other world-ending threats at bay.
The githyanki are sworn enemies of the illithids, but very much villains themselves.
The fey could be called upon to restore the proper natural order. However, they may take this chance to also get rid of the mark of man on the land.
An army of the undead would be immune to the psychic and mutating effects of the expanding region.


Tomb of Annihilation has an interesting version of this idea:Wow, does Kelemvor suck at his job or what?


I kinda did this with aboleths trying to bring parts of the world underwater. Humanity tried to create floating islands to survive.A bit of aboleth lore that I really like is how some of them regard their mucus as a symbiotic ooze, and pay homage to Ghaunadaur. So, in addition to raising ocean levels, they could try to turn the land into a slimy realm.

[Unoriginal]

Wow, does Kelemvor suck at his job or what?

Yes, yes he does.

But for this specific instance the one responsible is a bad guy who is known to mess with divinities and get away with it, so that explains it.

[Addaran]

Anything that self replicate, can convert people or reproduce by turning others is a great existential threat.

The Duun (?) In the new Disney movie Raya and the last Dragon. The xenomorph in Aliens. Agent Smith. Zombies, vampire, werewolf, though those are such a classic normal monster for DnD, most will just shrug at their mention.

If you make them weird, change a monster that wasn't like that or homebrew a new monster, it will be more credible and scary. The players also won't know ( or being able to check) that the monster is immune to poison, weak against lightning and have cha as his worst save.

[EggKookoo]

You need something that has an element that the PCs can interact with directly. A kaiju is a little one-and-done, unless it's the endgame.

So, something off the top of my head, not super-original. A disease appears, starting in remote villages. The symptoms are mild and not very different from most other illnesses. Mild fever, some aches, etc. Stuff most hardy folk can walk off but at the same time once you come down with it you never seem to really shake it. It spreads through the village, and people even talk about it, but no one really knows what it is aside from "the walking miasma" or somesuch. Then, once a threshold is reached in terms of pop density, everyone in the village transforms into... something. Zombies are the obvious trope but it could be more interesting than that. Maybe they take on some aspect of the village's culture, like if they're xenophobic, they become really violent toward outsiders.

So this thing is spreading through villages and the crown is worried it'll eventually hit a big city. Investigators (PCs) are dispatched to track down its source. Meanwhile, talk of purging villages begins to circulate. Ultimately it turns out the entire thing was orchestrated to do just that -- trick the kingdom into sanctioning the slaughter of tens or hundreds of thousands as a big mass-sacrifice in order to bring the actual BBEG across, perhaps with his demon/aberrant army or whatever he ends up being.

[Rater202]

Might I suggest a roving undead intelligence?

Basically, a sort of... Phenomena that happens when multiple mindless or feral undead creatures—skeletons, zombies, ghouls, ghasts, and anything that is of non-human intelligence or has an overwhelming compulsion to kill or prey on sapients—that are not under the control of a priest or necromancer congregate and sort of... synchronize.

They start wandering the countryside, any stray undead they encounter get.. Assimilated. Eventually it gets big enough that anyone they kill spontaneously reanimates as some kind of undead creature not long afterward... Then any fresh corpse they stumble upon... Then any member of the intelligence destroyed while a significant portion of it still remains gets back up as something...

Eventually, a roaming war party, a legion of the undead, marches upon the land and the first sign that anything is wrong is when the bones in the local churchyard burst from the earth and start to box in the living inhabitants so that when the rest of the undead intelligence gets there...

Men, women, children, pets, livestock, civilians, soldiers, the occasional unfortunate adventurer...

And, of course, the more undead that are part of the collective the more... Intelligent the collective becomes. Tactics become more refined.

One of them can be put down relatively quickly when discovered. A handful of miscellaneous zombies or a single ghoul accompanies by the clearly gnawed on skeletons of its victims are fine.

But a thousand skeletons and zombies, with fifty ghouls dispersed between them, an unfortunate Lich or Mummy that was assimilated to serve as a vessel of the roving intelligence's will, a disposable mouthpiece, and accompanied by dozens of ghosts, specters, wraiths, or what have you that are fewer the souls of people and more tangible manifestations of the aggregate desire of the collective.? That's a problem.

And when suddenly rumors of spontaneously reanimated corpses wanting of into the wilderness start popping up every week, the mass grave near a historical battlefield looks like giant tilled it like a garden, and encounters of roving groups of undead are reported with greater and greater frequency...

It's only a matter of time.

Someone needs to figure out what's going on and stop it before armies of the dead swallower the kingdoms of the living... Or worse.

Nobody wants to know what happens when two or more full-fledged undead intelligences encounter each other.

[Segev]

Dust mephits have declared war on all the other mephits, and indeed all other elementals. This may seem laughable, but as they win battles in the Material Plane, the other elements' influence wanes in the regions they fight. Areas are becoming dessicated dustbowls.

They are also winning far more than little stupid quasi-elementals such as them should be.

It turns out that a kobold entered into a dao genie pact (whether with a dust mephit or an actual dao is up to your story needs), and has been teaching them the way of Tucker's Kobolds and guerrilla warfare. He's a Pact of the Chain warlock with a dust mephit familiar (use imp stats, maybe give it the breath weapon from the mephit...or just let it be a mephit).

[Imbalance]

Sharn spell ends, Phaerimm escape, and the effects of their life draining spell begin to expand the Anauroch Desert at an alarming rate. Party is tasked with stopping a magical ecological catastrophe.

[Millstone85]

Might I suggest a roving undead intelligence?I dig it! *ba dum tss*

A variation of that would be an invasion of gibbering mouthers:

To quote this beautiful line from the MM, "as the last of a victim's body is consumed, its eyes and mouth boil to the surface, ready to join the chorus of tormented gibbering that welcomes the monster's next meal".
Van Richten's Guide to Ravenloft introduces the star spawn emissary and greater star spawn emissary. Lore aside, these are basically super duper mouthers complete with the ability to spit out regular gibbering mouthers.
Previous editions had a creature called the gibbering orb, a massive gibbering mouther with the levitation and eye-rays of a beholder. When two or more orbs met, they would merge into a single one which might later split into any number of orbs.

Edit: I don't have VRGtR with me right now, but it also stats the "zombie clot" and the "swarm of zombie limbs", both of which would go well with the undead-intelligence idea.

[Sparky McDibben]

I'd use the kruthik from Mordenkainen's. They're sort of presented like the Zerg, although you might want to beef up their abilities depending on player level. You might also reskin other monsters to fit into the swarm, like using mind flayers to emulate the zoanthropes from WH40K.

[loki_ragnarock]

Slaadi.

Beefy enough to wade through most guards, easy enough to kill for PCs that they can play the hero against hordes of them.
People they wound turn into more Slaadi, with art on page 276 of MM implying that the Slaad Tadpoles burst forth from the chests of their victims. They have tons of hp - relative to commoners or guards - and regeneration 10, so if you merely wound it it'll just come back again at full strength in under 2 minutes, and wounding them can be hard with their variety of damage resistance and their advantage on saves vs. spells. They don't need to kill people; they just wound them and retreat, relying on their bodacious regeneration to almost instantly recover from any wounds they receive in the process. For normal people, they represent an essentially unstoppable force; good thing, then, that they are relatively easy to hide from. But even then, even hiding, you might not be safe when a tadpole burrows out of the chests of your fellow survivors a few months later; it only has to happen once for everyone to figure it out, but once it happens... how few will be left to benefit from having figured it out?

Run them like Xenomorphs; incredibly difficult to kill aliens that will replace your entire species.

And that's just the Red Slaad. The Blue Slaad has a damage threshold on it's attacks that means it just kills small time people with one blow, as things guard tier and lower just die. No... the Blue Slaad is worse, because it converts only those who have the ability to actually defend against the Slaadi incursion. Your heroes. Your champions. A wound changes those people any community would rely on to defend them and makes them the enemy, and so much faster than those who survive the Reds.

The Green Slaad don't cause their victims to turn into your enemies. No. They're *worse*. They become your friends with their shapeshifting powers. The Reds and the Blues are easy to hide from, at least. But the Greens get welcomed in. The damage from that is more, worse than the simple fact that there is an infiltrator that can expose whatever groups of people have managed to hide, either turning them in or picking them off one at a time. No, what's worst is that it makes it so that the only groups of survivors that don't get infiltrated are the groups without the compassion required to save their neighbors. That means what dies isn't necessarily all of the people in a population... just the concepts of brotherhood, compassion, and unity that would be required to mount a decent defense. Green slaads don't make the people they strike the enemy. They instead induce paranoia, fear, and mistrust. They make everyone the enemy.
And on top of that? Detect Thoughts. At will. You can't hide from a Green Slaad once it's near you. They will find you.

Grey Slaad are a more subtle departure from the Green. Their passive perception is such that it's *very* hard for normal people to escape detection, in addition to the Detect Thoughts trick that the Green already have. They also can go invisible at will; Grey Slaad aren't Xenomorphs. They're Predators. Except they're also T-1000, because they can change form however they wish, much as the Green Slaad, transitioning between a visible friend and an invisible enemy on the fly. And because - much like the green slaad - they play no role in the Slaadi reproduction cycle, they're just there to kill. These ones are the agents of annihilation, the Slaadi that make the entire world your enemy. Is that path as safe as your eyes say it is? The Green Slaad made survivors not trust each other. The Grey Slaad means they can't trust *themselves.*
Also, they can fly. Makes it hard to hide *and* run.

Death Slaad are basically Grey Slaad with more hp, more damage, higher spell DCs. They don't add alot to the creeping horror of extinction except making it faster.



From a practical perspective, Slaadi also hit that CR sweet spot so that you can slowly introduce them as a dangerous threat one at a time while still allowing for higher level parties to deal with hordes of them as they come into their badassdom.

[BoutsofInsanity]

The Slaad are great.

For specific monsters that serve as a BBEG I like the following.


An Evil Party - Nothing is scarier than other adventurers. Stat out an evil party and have them go to work.
Give a Lich Monk levels and a better Wisdom Modifier. A lich that has the defenses and acrobatics of a monk and full casting, who also has stats for diplomacy and such should be terrifying.
The Slaads are a good choice
I'm always a fan of Demons
If you can swing it. The Star Spawn are awesome and herald in your eldritch horror

[Trafalgar]

Try Zee Bashew's version of the Kua Toa. It leads to the emergence of a new god.




https://youtu.be/hF83hrcaJTA

[Unoriginal]

You could also have an existentialist threat monstre. Like a Monk who forces people to confront reality outside of all its illusions, and since they have not trained to reach enlightenment the people just die or are erased (or their minds are, at least).

[Dalinar]

Our current campaign involves a powerful spellcaster (specifically a druid) that found an ancient artifact that can mass-produce simulacrums, made heavy use of it, and was betrayed by the simulacrums that felt they got a raw deal. Of course, simulacrums aren't long-lived, but they keep churning out more of them, and they can pretty much only survive by pillaging for healing potions and the like, so...

I like how it's a cautionary tale about misuse of what's arguably the most powerful non-Wish spell in the game.

[greenstone]

Monsters that replicate themselves with every victim.

Yep. A nanomachine grey goo apocalypse (https://en.wikipedia.org/wiki/Gray_goo), but with something like shadows instead.

A yellow musk creeper could do it (from the 5E book Tomb of Annihilation). Imagine triffids, but instead of blinding people, they enslave them.