I've decided to throw "Death House" at my players as a one shot on Halloween night. My only problem is that they are level 10’s and death House is designed for first level. Has anyone done something like this before? I'm using the DMG to level up the monsters, but I'm worried it will feel weird for my players.

Thanks!

Andy

Rather than leveling up the monsters, you might choose to swap them out altogether. The final boss could be something like an Atropal and the smaller encounters along the way would similarly be swapped out for an appropriate higher power alternative. This would at least prevent the players from feeling like they're fighting a modified stat block.

Treasure would also need to be scaled appropriately. Other than that, nothing about the story really needs to be changed.

For the sake of flavor, you might embellish the house itself to make it appear more lavish and menacing to account for the higher level occupants/treasure.

Well, since it’s a one-shot, why don’t you just have the players create new characters just for this game? (That’s usually what one-shots are anyway, and it might be fun to switch it up.) There’s also an old article buried in this website’s archives called “Strahd Must Die Tonight,” which tells you how to run Castle Ravenloft, which is intended for 10th level, in a single night. Good luck!

I can speak from experience.  I liked that module but my players were already level 6-7.  One thing I had in my favor was I had plenty of time to set it up.  One of my characters was a disinherited noble and he received a nice shiny mansion in town in exchange for doing some dirty work for the local Duke.  Of course, this house was haunted and I was able to give him some out of game updates from his housekeeper and guard retainer about crazy shenanigans in the house.  When I was ready to run it (around level 8) I just had things go bonkers such that the player reached out to the rest for some help in getting to the bottom of things.

Instead of just leveling up the monsters, I went more "escape-room" and atmosphere.  I think there was actually a lot less combat.

I homebrewed an evil fey spirit to be the haunter... a "collector" type boss who had tiny cages on the ends of chains.  Each time a player was hit they had to make a save or they disappeared and reappeared as a tiny hommunculis of themselves inside one of the cages.  Once he captured enough of the party the boss was going to open a portal and bounce out of there with his new toys.  My players destroyed it in time and then had to take the little PC trapped in a cage and figure out how to restore him.   That might have been the only "major" fight in the whole house, though I know I added more traps and there may have been a banshee upstairs.

But mostly it was just psychological horror.  Rooms changing if they entered them multiple times.  They couldn't leave the house.  One time when they called out to some commoners on the street through a window, the commoners all froze and a spectre came along and murdered them all one by one before coming back to the house (this was just an illusion).  Windows in one room looked out on the city at day time.  Other windows showed the city at night, or after some horrible flaming holocaust.  Later the players wound up trapped inside the dollhouse as miniature versions of themselves (as a foreshadow of the boss' special ability).  And all through the house, the evil spirit was talking to the noble PC and negotiating with him for handing over his companions in exchange for a warlock-patron relationship.  The other PCs knew he was talking to something but he wasn;t honest with them about it and seriously considered the deal before ultimately deciding he couldn't trust the monster.  

Oh, and the suit of armor (animated in the module) was a red herring.  I made a possessed chandelier the real threat at the top of the stairs.

It was fun.  I highly recommend it.