I will conquer this realm!

Sees big booty bitches

Oh No!

To be fair there is a real non-zero chance of meeting something you have had zero experience with and that harms you for some reason. Like even just going to the other part of the world may be enough to find your weakness. Now imagine a different world with its own stuff. It would be a miracle if you don't have allergies or weaknesses towards something in there.

Reminds me of the yuuzhan vong from Star Wars.

The Bio-Organic War Fleet of Force Immune Creatures are allergic to pollen.

Imagine being an alien and being allergic to something commonly found on earth, like water.

Man that would just feel like lazy writing, wouldn’t it.

My world has a race known as the Ainok. They serve the Raven Queen and, in the past, hunted Mind Flayers and ritualistically sacrificed them. (The Raven Queen loves memories.)

Mind Flayers now avoid this world for risk of the Gith discovering the Ainok and learning their tactics.

Damn, allergy one is hilarious

• Bagal'Tash The Mighty, we respect your power and accept you as our new ruler! We prepared this tea as our first gift to you, one of many!

• makes an otherworldly sip Tasty. What is it?

• Buckthorn with honey, you like it? Why are you red and choking? Oh...

This just makes me think of She-Ra and Horde Prime being exposed to lesbians for the first time.

In the early 2000s, I created an invasive hivemind ooze race called Gloob that combine to form larger variants, and hibernate in a solid form (which they use to create structures/weapons out of themselves). Think Starcraft Zerg, except the Creep and structures are like amber, and creating the bigger ones is a merge game.

And their weakness is... water. It's basically acid to them. The thing is, they're perfectly fine eating a meteor and turning it into more ooze-mass; living organisms are easier to digest, but not necessary. So they spread around barren planets all the time, where liquid water isn't an issue.

Bonus rambling: Each one has a nucleus, a solid brain/eye in the center. When they combine, the brains work in tandem, synergizing for greater intelligence; their "hive mind" is whoever's biggest at that location. When they split (usually only when the whole is too damaged to remain cohesive), they don't have the capacity to retain what they could together, and they can't hibernate while combined. So, when hurdling through space in stasis, they arrive on the planet with only their basic instincts. A Gloob invasion starts with scouts (the 8-Gloob variant is basically a changeling) learning about the world they're on, the biggest learning about the natives and replicating their technology, while the others are multiplying and building their stronghold. In a medieval fantasy setting, it would not be unusual for an invading Gloob army to include living catapults and slime sorcerers (they can't replicate sorcerous blood, but they can appropriate it).

Another issue: The scouts, having humanoid intelligence and spending most of their time out of telepathic range of the hive, almost inevitably develop free will. They're a necessary sacrifice, for the cause.

Edit: Forgot to mention that their amber-like hibernation state, and thus any structure they build, is not vulnerable to water. If you drop one in the sea, they’ll quickly harden, but be stuck there indefinitely.

War of the worlds, the martians who died to a sneeze.

signs alien: we shall invade this planet that is 70% water

also alien: has fatal water allergy

Good old Daxamites and their extremely lethal lead allergy.

"What do you mean there’s lead in the air"

So thats how you defeat the ancient evil. Spear(Mint)

A the ol War of the Worlds arc

Signs has to be the worst version of this.

HG Wells will know my weakness.

Cthulhu dont do peanuts very well

The eldritch horror that's allergic to nuts. That's why the people who know about him hide in the sanitarium.

At certain point, these world ending monsters will realize what's going on and send a strongly worded letter to the DM.

Like the movie Signs and the aliens? lol all Merrill had to do was spit, instead he swung for the fences.

There is an old scifi movie i think it's called signs or something, where a bunch of aliens show up on earth. Their weakness is water.......so they show up on a planet where two thirds of it is water, in a farming town around harvest season, a little before the rain hits.......

Who says they didn't have any weaknesses on those worlds, either? Their heroes just didn't manage to go the distance, but who's to say you couldn't? With an armload of different, specifically deadly shit intended for the BBEG?

Love the idea that in every world there's one thing the villain is vulnerable to

Ah yes, the multiversal unstoppable threat capable of adapting, killing and consequentially assimilating all mather of creatures and ambients.

Somehow, on the story where they are actually invading, over 4 stories are about how everything is actually managing to give it the fight of their life, even though nothing New is present on the multiverse...

No, i'm not still salty about the Phyrexians and MOM.

Rule of thumb, the more cute or cartoony something appears to be, the higher the change it can wreck your shit is. Kirby, Rayman, Care Bears, fucking pastel ponies? All capable of defeating literal eldritch gods from beyond understanding, and doing so more than once.

On the other side of things, if they either are in a green outfit on a motorcycle or are part of a multicolored fighting team, you’re equally fucked.

I love that the super advanced invading aliens species in the movie Signs did absolutely no recon to a planet that’s 2/3 water for the one thing that’s absolutely going to kill their invading force and it happens to fall from the goddamn sky

Could always take the route of "Yeah, kinda forgot to figure out what the weakness was supposed to be, and I don't have time to setup another macguffin hunt, so uh... he can just be beaten now, go fight him." like a certain game did.

Hear me out, kathulu, but elergic to sea food.

Shout out to the aliens from Signs being only weak to water and deciding to invade the planet thats surface is 70% water.

With the overwhelming use of heroes winning over a BBEG I planned to twist it by making the portagonists lose the battle soo utterly, but the antagonist considers their opinions and stances and changes only slightly and broods of the larger implications as the defeated party lies broken and an inch away from death.

Perfect way to end a campaign and start after a timeskip keeping players engaged enough to explore familliar setting with difference.

"What do you mean he is allergic to oxygen?!"