Devilish DM tricks

>new group
>party wandering through forest
>ask me if they see anything interesting while wandering through
>tell them to roll a dice, they get a 20
>tell them they find some random old man
they spend the next 6 months of the campaign taking care of him and making sure his senile ass doesnt run off , convinced he must be secretly a really important entity since they rolled a 20 to find him.

Magnificent

Inspired by hypercube dungeon maps of /teej/ fame, I'm planning a one shot with a 4 dimensional monster. The dungeon will appear conventional at first, but inside they'll find an artifact that will let them move through the fourth dimension to chase it.
The best part is that I won't tell them it's four dimensional, and see if they can figure it out based on what they see throughout the dungeon.

Too far if the player has gone through a bad breakup in the last 12 months.
Drop some hints about her true personality. Having an NPC rob a PC usually diverts the campaign into Revenge-murder until one or both sides have died.

I haven't run a game in fucking years, but I ALWAYS used modular rooms, monsters, and items. I'd just plop them down into wherever the party was going next rather than meticulously craft everything beforehand.

The players won't think that it's railroading unless they peek at your laptop.

I always make a single NPC in the party's starting town or city a werewolf, changeling, vampire, ect. Some kind of non-human or monstrous human masquerading as a regular human. Usually someone the party will be interacting with alot, like a shopkeeper or merchant. They will always been an alchemist of some sorts or friends with the town alchemist, and being using potions to help control their "condition", which I will drop subtle hints about during the campaign. I will also drop other hints such as animals being tense or avoidant of them, and the NPC doing things like travelling alone or going out at night unarmed and seemingly unconcerned for their own safety.

I've still never had anyone figure it out before the big reveal. I've had a few players suspect the NPC was a warlock and doing dark magic though, incorrect as that guess is.

Oh fuck I might do this. They love the Mayor, let's fuck with the Mayor.

I find it helps if the NPC themselves isn't explicitly evil. Like, the last time I did this, it was with the town's alchemy merchant, and she had been kidnapped by bandits while getting ingredients in the nearby woods (again, animals animals avoided her because animals could sense she was a werewolf). By the time the party found her, she was midway through tearing the bandits apart because it had been too long since she had her last dose of wolfsbane potion to keep the transformations suppressed. When the dust settled, the party was now faced with the choice of letting her go because they liked her and she had never brought anyone in the town harm... but also had to deal with the fact that it would mean keeping everyone else oblivious to something that could be extremely dangerous in their midst (as the town probably would have lynched her if they knew).

DESU I'm not really a fan of forced moral choices for the sake of forced moral choices, so maybe avoid this if there's a smitebot paladin in the party or the party gets mad over deep moral stuff... but if you're looking to make the encounter more meaningful than a combat to be beaten and forgotten about, this is the way to do it.

well, it isn't really.

>Later, bitch on Veeky Forums about how your players are a bunch of murderhobos you’ve trained to never let anything live.

Plus points, have it being in a horro, or at least dark fantasy game.
So far every parody of humanity has been a
megalomaniac tyrant.
Just to fuck with their heads, after all they should never get their feet too long on the ground in a good game about horror.