D&D 5E Share Your Meanest, Most Dastardly Trap

[Reynard]

With the new UA all about implementing traps in 5E, I figure here and now is a good time for us rat bastardly DMs to share our favorite traps we have sprung on parties.

Most recently I sprung the "Elevator to hell" on a party. The elevator looked like a normal wooden lift going from the sub basement to the citadel above. it was, of course, a trap to kill interlopers. Hidden by the wood was an iron cage without a floor. Once the PCs entered the lift and pulled the lever, the cage slammed shut. Above, a glass cage shattered and a gelatinous cube was released. it burned through the ceiling in a couple rounds and slid through the cage to fill the lift. The PCs were immersed in the cube for another couple rounds until it burned through the floor, which revealed a 50 foot shaft to poisoned spikes where anyone that survived the impaling and the poison continued to be melted by the remains of the cube.

 

[Nebulous]

In 4e, I remember there was a trap that killed the 9th level barbarian in 2 rounds. The floor shunted him into a chute, and there was an otyugh and rats at the bottom of the shaft. It happened so fast, his allies didn't even see him disappear, and never saw him again dead or alive!

 

[Reynard]

It has been a while since I have done anything with lava. I should spring some lava on my current party...

 

[Cap'n Kobold]

"These doors loom over you; over three times your height and wide enough to drive two carts through. They are made of a heavy, dull metal; possibly a lead alloy designed to block magical scrying as well as physical assault. The only ornamentation is a small plaque with a stylised chest and sword on it. There are two recessed handles; one on each side of a large keyhole."

The doors require at least three people to open: both handles must be pulled before the lock can be unlocked or picked. This also disengages the hinges at the sides.

The actual hinges are along the bottom edge of the door.
There is just a blank wall on the other side.

 

[iserith]

I designed one recently where a huge boulder drops from the ceiling on an area of the dungeon that has a declining floor. It rumbles along behind the PCs, picking up speed as the corridor turns in upon itself in a spiral before ending at a pit which drops into an underwater maze. The corridor through which the PCs are likely running contains areas of difficult terrain, a slippery grease trap, grappling zombies, and a flame jet trap. (Did I mention the grease makes the PCs and the giant rolling boulder flammable?)

Those PCs that can stay ahead of the boulder despite all the obstacles in the way end up at the center of an unlit maze that is completely underwater, floor to ceiling. At some point, that rolling boulder from the level above falls through the pit and, given the dimensions of the chamber at the center of the maze completely fills the room. This potentially pushes the PCs through one of four doors in the chamber, splitting the party. Now it's a race against time to find the way out of the maze before the PCs' drown. This entails finding a sealed door that requires some effort and skill to open. Along the way, the PCs may run afoul of a ghostly sea serpent that can phase through walls.

 

[Reynard]

"These doors loom over you; over three times your height and wide enough to drive two carts through. They are made of a heavy, dull metal; possibly a lead alloy designed to block magical scrying as well as physical assault. The only ornamentation is a small plaque with a stylised chest and sword on it. There are two recessed handles; one on each side of a large keyhole."

The doors require at least three people to open: both handles must be pulled before the lock can be unlocked or picked. This also disengages the hinges at the sides.

The actual hinges are along the bottom edge of the door.
There is just a blank wall on the other side.

Splat.

 

[Reynard]

I designed one recently where a huge boulder drops from the ceiling on an area of the dungeon that has a declining floor. It rumbles along behind the PCs, picking up speed as the corridor turns in upon itself in a spiral before ending at a pit which drops into an underwater maze. The corridor through which the PCs are likely running contains areas of difficult terrain, a slippery grease trap, grappling zombies, and a flame jet trap. (Did I mention the grease makes the PCs and the giant rolling boulder flammable?)

Those PCs that can stay ahead of the boulder despite all the obstacles in the way end up at the center of an unlit maze that is completely underwater, floor to ceiling. At some point, that rolling boulder from the level above falls through the pit and, given the dimensions of the chamber at the center of the maze completely fills the room. This potentially pushes the PCs through one of four doors in the chamber, splitting the party. Now it's a race against time to find the way out of the maze before the PCs' drown. This entails finding a sealed door that requires some effort and skill to open. Along the way, the PCs may run afoul of a ghostly sea serpent that can phase through walls.

I like this especially for how it produces an every increasing difficulty upon the party. they have to keep moving lest the boulder catch up to them, and that means taking less time and care than they should while moving through the dungeon. I am inclined to yoink a good bit of this design.

 

[iserith]

I like this especially for how it produces an every increasing difficulty upon the party. they have to keep moving lest the boulder catch up to them, and that means taking less time and care than they should while moving through the dungeon. I am inclined to yoink a good bit of this design.

Yes, it gradually escalates until you reach the underwater level, then you have a whole new set of problems to deal with. What I didn't mention is that I also included treasure in niches along the corridors of both sections of the dungeon and it takes an action to pry the treasure loose. So now you have competing priorities as to how to spend your actions on top of everything else. If you're ahead of the boulder or have air remaining, do you risk grabbing treasure?

 

[mellored]

A glass maze filled with hallucinatory fog.


The glass easily breaks with 0 AC, and only 1 hit point, but it is immune to fire/cold/electric/psychic/radiant/necrotic damage.
Any player who walks at full speed into the glass breaks it and takes 2d6 damage, as well as 1d4 damage for walking on broken glass.
Inside the glass are illusions of monsters. They roll initiative as normal, and they attack anyone who enters, but they always miss.
There is a short section of glass maze outside of the fog, which does not contain any illusions. Just enough so they know that it is a glass maze and running around inside is dangerous.
The fog gives everyone disadvantage to hit, makes the glass invisible, and makes the illusion attacks seem real, though they still always miss.
Breaking glass transfers the illusion of the monster onto the breaker (break the kobold illusion, and you become the kobold illusion). This illusion ends when you exit the maze.
The glass repairs itself after 2 rounds, and now has the illusion of the person who broke it, (which proceeds to attack and misses).

Countermeasures:
Just walk though slowly. Any damage is self inflicted.

 

[Mad_Jack]

A large mirror dominates one wall of the room. On a shelf below the mirror is a small oval-shaped device made of what appears to be porcelain and of a size suitable to put a hand atop. It has several buttons inlaid on the sides.

A spell laid upon the mirror forces anyone within twenty feet of it to succeed on a DC 18 Wisdom save with disadvantage or be charmed into gazing into it. The character will immediately move adjacent to the mirror and lay their hand upon the device below it. If another character currently has their hand upon the device, the character will simply approach the mirror and gaze into it, slack-jawed and unresponsive. A character who succeeds on their save cannot be affected by the mirror trap for one hour.
Once per hour, a character trapped gazing into the mirror may make a new DC 18 Wisdom save with disadvantage in order to pull their gaze away from the mirror. Anyone not affected by the mirror may use the Help action to cancel out the disadvantage on the saving throw.

Although anyone standing more than twenty feet from the mirror will see only the usual reflections, when someone comes within twenty feet they (and only they) will see that the mirror contains not the reflection of the rest of the room, but an image of a piece of parchment or a page from a book.
The title of the document shown in the mirror reads...

"TVTropes.org"