Playing d&d, really want to do "the thing" campaign.

An entity from the outer planes that has the ability to inhabit the bodies of the dead and cast a variant of the polymorph self spell. It has the unique property copying the original so well that it doesn't even know it's the entity until attacked or it needs to feed again.

It can only be killed with fire or magical weapons.

>>53920424
the thing is a secret elf

>>53920424
>Isolated location.
>One of the NPC's (or even PC's depending on your group and DMing style) is a dangerous creature in disguise.
>Create a "whodunit" mystery plot hook.

>>53920523
How do you get your players paranoid enough without having them just decide to sit in a room together all day?

>>53920424
I strongly recommend looking to the Book of Elder evils for some inspiration. Even if you're not running 3.5, there's some good reference material in there for at least story. Notably, Ragnorra, the Mother of Monsters who's a being that's overcharged with Positive energies.

>>53920563
Create a sense of urgency or time limit to the situation. The Thing is set in Antarctica to not only isolate the cast but create a sense of urgency. They can't run away, they have to find
and destroy this thing or they die.

>>53920594
Not to mention the fact that they need to kill it before it kills all of them, and then eventually makes it back to the mainland where it can start assimilating the masses.

>>53920563
Food's running low and they need to get more. Fire Breaks out. The ship's hull has sprung a leak or twelve. Loud banging nearby. The dogs are going nuts outside. Ramirez has a flamethrower and we can't find his meds.

I've got a good group, I'm thinking of bringing them into another room one by one and explaining to them that they think somebody is a monster imitating them. Obviously I would tell one of them that it's them, and they need to all figure out what's going on.

I need to figure out how to split them up periodically, and what the end goal is. How do they discover the monster? What's the monster trying to do? I can't have it attack people eight off since it'll give everything away.

>>53920424
I'd use Dread.

>>53920770
This is the correct answer