Illusion and Darkness

[Thorongil]

So I had an idea for a terrifying encounter, but I'm not sure how to construct it with RAW in such as way that it's both legal (or close enough) and won't be broken by players metagaming.

Long story short, the party goes to investigate an Aztec hideout (Caribbean setting), looking to recruit some people. When they arrive, there's a large cave mouth set into a cliffside, with a small idol carved into the rock overhead. Inside, they see a completely innocuous cave. Moss, maybe a creek, some insects and rodents.

What they don't see (or can Save to see) is a big honking illusion that the Aztecs placed over the cave. Beneath the perceived reality, the cave is lined with murder holes, pits, and branching tunnels, so that the Aztecs can just pick off any Spaniards or beasts who come looking.

But the Aztecs aren't home anymore- turns out they put their hideout on top of a monster's lair. I'm not sure yet what sort of monster it out to be, but it should be good at sneaking, grappling, and it should have a strong desire for human flesh. Bonus points if it's humanoid and large/huge, since this encounter idea is rooted in Fransisco Goya's painting Saturn Devouring his Son (https://en.wikipedia.org/wiki/Saturn_Devouring_His_Son)

Longer story shorter, the monster picked off the Aztecs one by one, sneaking around in the tunnels and getting the jump on them with superior hearing/smell/blindsense.

The mechanic I’d really like is for the players to be walking along, and suddenly realize that whoever was walking in the back is gone. That player feels a very large hand grab them, and apparently pull them right through the wall/floor/ceiling. They wake up hogtied or caged next to a cook pot.

So- is this doable, and how is it doable?

EDIT: I forgot to mention, the party is 6 players, and they’ll likely be around level 7-8 when going through this.

[Unoriginal]

I suggest a Large Choker who has the power to go in the Ethereal Plane and to drag the people it grapples in it too.

Though be sure to actually do it by the rules: attack rolls, etc.

Just pull the players whose PC is the target aside, and if they get grabbed don't tell the others what happened.

[DrowPiratRobrts]

https://www.dndbeyond.com/monsters/50412-sasquatch

I found this and it seems like a good place to start for the creature. If Adv. on perception isn't good enough you can always give it blindsense 60 or something. Feel free to edit the monster however you want to make it fit how you want.

I like the idea of the encounter with the monster. Maybe as they explore don't suggest that they roll perception. Just use there passive vs the creature's stealth. If it fails a few stealth checks, tell the party they hear some noises throughout the cave of rocks shifting or something like that. Because there's an illusion and it's a cave they will be disoriented. But at least they'll know they aren't alone if the creature fails a stealth check or two. Once the creature thinks it's got the jump on them, have it swipe the last person in a narrow corridor. Don't say anything, just slide a piece of paper to that character and have him/her read it secretly. If the rest of the party asks that PC a question the player can't respond (you can note that on the written message). They'll figure it out sooner or later.

To make the above possible without getting into combat, you can give the monster an "Abduction" ability. Once/day in it's "home/domain" it can incapacitate one creature of equal or lesser size in one swift action. The target wakes up in 1d12 minutes (should be plenty of time for the creature to get away and restrain the PC).

Note that you run the risk of upsetting the kidnapped player, so I'd suggest flashing back to them occasionally once the party realizes they're missing. Allow them the opportunity to work on an escape plan while the creature is hunting the other party members. This should give them something to do and I don't think they'd be too upset about the interesting challenge if they haven't lost a ton of HP or resources.

[DMThac0]

And the Underdark, my beloved, comes to mind almost immediately!

Fomorian, in it's natural statblock has a +6 STR, Darkvision, considered Huge, and is a pretty nasty critter, however it is also CR 8. Check it out and see if it fits.

The illusions that you refer to are easy enough to make difficult by setting a DC 25 or some such thing.

Keeping the players from saying "Jinkies I've been kidnapped", is also an easy fix. With a simple post it note or text message saying "roll an athletics/acrobatics and write/send me the result". You'll roll at advantage as long as they've not seen through the illusion (refer to the obscene dc), and you'll most likely succeed in the grapple. Otherwise, if you need at least one player to be kidnapped, just make it happen. Send them back a post it/text saying "you cannot tell anyone: the world is dark, your mouth is gagged, and you're no longer able to move." This should work for at least 2 players, you might get 3, but it will become obvious quickly if your players are observant enough.

[DrowPiratRobrts]

And the Underdark, my beloved, comes to mind almost immediately!

Fomorian, in it's natural statblock has a +6 STR, Darkvision, considered Huge, and is a pretty nasty critter, however it is also CR 8. Check it out and see if it fits.

The illusions that you refer to are easy enough to make difficult by setting a DC 25 or some such thing.

Keeping the players from saying "Jinkies I've been kidnapped", is also an easy fix. With a simple post it note or text message saying "roll an athletics/acrobatics and write/send me the result". You'll roll at advantage as long as they've not seen through the illusion (refer to the obscene dc), and you'll most likely succeed in the grapple. Otherwise, if you need at least one player to be kidnapped, just make it happen. Send them back a post it/text saying "you cannot tell anyone: the world is dark, your mouth is gagged, and you're no longer able to move." This should work for at least 2 players, you might get 3, but it will become obvious quickly if your players are observant enough.

I like your idea of going for multiple PCs. Harder to pull off, but if two of them wake up in separate cages that would be gold.

[Segev]

I believe they're in the 5e monster manual, but they aren't in the SRD so I could be wrong: Spriggan Gnome. They can, as an action, grow from Small to Large (or revert back), and have excellent stealth capabilities when small while being good combatants while large.