One great thing I love to add when designing a dungeon is a dead adventurer. It's a very versatile piece of set dressing that can really up the feng shui, really tie the room together. But seriously, you can do a lot with a dead body.
If you want to signal to your players that this place is dangerous a dead adventurer is as good as a blinking neon sign. A pile of bones shows that something in here is a carnivore, a human skull says maybe people were entombed here or this thing got a commoner, but a corpse in full armor with a sword and shield tells the party that people like them have died in here. “Hey, doesn't this guy look a little bit like the fighter?” Now they're aware of their own mortality.
To show your party that they need to be on the look out for traps, show the aftermath of one. A low DC medicine check shows the deceased laying in front of the creepy statue was crushed under a great weight, or burned up in a fire. I'm not sure if these dayglo mushrooms are poisonous, but they sure are big and there's a skeleton in rusting armor beneath them.
To show the party there's a big fight in the next room, put a dead adventurer in the antechamber. Have a potion or two in their pack and at least one of your players should get the message.
A DM can deliver plenty of other information with a dead adventurer as well. It could have a map in its pocket, to this place or a whole different location where another adventure awaits. Or they could have a journal with just enough back story to contextualize exactly what the players have walked into here in this dungeon, or what is going on in the wider story of the game. If you're clever this can also encourage map making and note taking among your players. The map is incomplete, or there are blanks to fill in on this bad guy org chart.
You can even get fancy and make a handout for this, which is a good idea if this is going to be more of a full on data dump than a couple of clues or bullet points. “You find a short sword, 47 gold pieces, and a small book on the ancient history of the war between giants and dragons, I texted you the file.”
It's also just a great and simple way to deliver treasure. “I'm not sure the Troglodytes living in this cave had a bustling economy with a lot of wealth and magic items, but looks like they killed this dwarf adventurer and he was rich!”
This dead NPC can also point the way to live ones with plot hooks. Maybe they were part of some faction that will reward the PCs for bringing back news of their fallen comrade and have info and quests. You can be direct or subtle with this. “The dead adventurer carried a highly decorated +1 shield,” or a magic necklace or bracelet, something enticing enough that someone is sure to pick it up and wear it. Then deeper in the dungeon, or the next time they are back in town, some acolyte or knight or spy recognizes the symbol on it and is very interested in the party. Maybe this NPC starts talking to them as if they are a part of their group, super friendly and dropping secret knowledge. Or maybe they are openly hostile, “you're not one of us, where did you get that?”
There are a ton of creative uses for a dead adventurer, maybe drop one into your next session and let us know how it goes.
