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Not all dungeon crawls are created equally. A dungeon can either challenge players and provide classic fun, or it can turn into a tedious slog of a death trap that completely frustrates players. What makes the difference? There are three things that make a good dungeon run: storyline advancement, worthy reward for risk, and fairness of traps and encounters.
In this article, we’ll focus on the last point: fairness in traps and encounters. Some DMs would argue that traps are a waste of time (I know a few players who would agree as well). Whether you’re building a dungeon or spicing up normal situations, consider the following points for building mechanical traps.
Stay tuned for a table of mechanical traps at the end of this article!
A Caution on Traps
My experience has been that traps often do not add value to an adventuring day. Traps tend to slow a party down; players become overly cautious or avoid areas that may give them trouble. Use discretion and make traps more meaningful by using them to advance the plot. Do not sacrifice plot in a dungeon: it is one of the three rules of a good dungeon run!
You can also speed up the party by giving them a heads up about the traps they may encounter. Maybe a note is nailed to a tree, warning them about specific traps; or perhaps the local constable is familiar with the skills of the tinkerer villain and set your party’s expectations.
Remember that traps are fun, but providing a fair, succinct adventure is what makes a memorable experience for players.
What Makes a Successful Trap?
Each successful trap requires 6 elements: a reason why the trap exists, a trigger to spring the trap, a difficulty class (DC), an effect, a way to disarm the trap, and the damage or result.
1. A Reason Why. If a player is strolling through a forest, why would a crossbow be armed in the elbow of a tree to spring on the unaware passerby? A good answer to this question could advance your plot, introduce new non-player characters, and develop players’ skills. Perhaps a band of kobolds is hoping to get the jump on their next meal, or perhaps the crossbow is a forest gnome’s quick attempt at protecting himself from being chased. Before you throw in a trap for a trap’s sake, think about WHO put the trap there (and what level of skill they would have in trap-building), WHY they would want a trap at that specific place, and HOW this person set up the trap (is this a trap that requires more than one person to set up? What materials are required?). These questions will guide you to better trap-building.
2. A Trigger. Using the crossbow example again, what sets off the trap? Does your party stumble over a tripwire? Did the barbarian step on a pressure plate? Note that triggers can make sense based on terrain, and some triggers don’t mechanically make sense for the trap. Another thing to note is: does the trap reset itself? Does an NPC need to reset it? See the table below for ideas on triggers.
3. Difficulty Challenge. This element is especially important for a DM to consider, as a too-difficult trap will frustrate players, and a too-simple trap will be brushed aside as a waste of time. The table below should give you an idea on balanced traps in terms of difficulty. You could allow your players to make rolls to perceive hints or elements of a trap, or you could force them to roleplay how they avoid, see, or react to a trap. One thing that frustrates players the most is being blindsided by a trap without any indication that they’re running into a trap. As the DM, it’s your job to give players every chance to experience the world around them as if they are in the actual world. Thus, alluding to a trap without giving it away is a great tool to mitigate players’ wrath. When you’re building a trap, think about what hints would exist to tip off the players: do they see the tripwire gleaming in the light? Maybe the short gnome would notice it easier than the half-orc.
Additionally, how do you help the players react to traps before forcing the effects upon them? The Angry DM wrote a great (lengthy) article on giving your players a chance to act in the split second they realize they sprung a trap. Going back to the crossbow example, as soon as one of the players feels the pressure from the tripwire on their ankles, or as soon as they hear the clicking sound of the crossbow, give your players a quick single action to do something to react: jump aside, hit the deck, put up a shield. Their actions may not always reduce the damage, but at least they were given a choice to do something.
4. An Effect. This element is self-explanatory: the tripwire releases the latch that holds the bolt and shoots it forward, potentially hitting a player. But what if there were more effects than just the obvious? The sound of the crossbow alerts the kobolds who set it up that their meal is dying a few feet away; or the yell of pain from a player causes an NPC to meander to the party’s location. The “effect” can cause a chain-of-events that ties in to the reason behind the trap, the storyline, a player’s backstory, etc. Make your traps more meaningful, and I guarantee your players will find them worthwhile.
5. Damage/Result. Finally, your players stumbled across the tripwire clumsily, failing their dexterity saving throws, reacting inappropriately, and one person gets hit with a bolt. What happens next? Maybe a player takes 1D6 of damage. Maybe the bolt hit him in the bag and damages an items. Maybe the bolt was dipped in poison, and he becomes ill. Did the trap fulfill its purpose? Do the kobolds come rushing in, forcing your party to leave behind the player’s torn item? Be aware of the level of deadliness a trap has, and be aware of the additional results upon springing the trap.
6. A Way to Disarm. Players love to make choices. That’s why they’re playing. They want to do something cool that saves the day. So why would you make a trap that they are doomed to suffer from? Give your non-star players the chance to notice the tripwire, or to examine the crossbow and figure out how to disarm it. Sure, they still have the chance to fail and activate the trap, but maybe messing with the trap activates it in a different way than they were expecting and causes a whole chain of unexpected events.
A Note on Xanathar’s Guide on Traps
Wizards of the Coast’s 2018 Dungeons and Dragons manual, Xanathar’s Guide to Everything, revisits traps in a refreshing way. The best tip I could reiterate from this guide is to take note of players’ Passive Wisdoms early on, then, if their wisdoms exceed the DC for a simple trap such as a pit, describe what they start to see, but don’t give away or completely explain it. Let the players examine the trap and figure out for themselves how to counteract it. The table below will use inspiration from Xanathar’s ‘Traps’ section to describe some basic mechanical traps.
Here is a table of the five elements above for your easy reference.
Note that this table will not render correctly on mobile. We recommend using desktop!
| CR | Trap | Description | Reason (Who, Why, How) | Trigger | DC to Notice | Effect | How to Disarm | Result |
|---|---|---|---|---|---|---|---|---|
| 1/8 | Pit (not hidden) | A pit in the ground, deep, but not hidden | Discourage traffic toward a destination or reroute traffic | Step into hole | Perception 10 to notice | Fall 10 feet | Walk around | Fall damage, injury, trapped |
| 1/8 | Portcullis | The portcullis is held in place by a series of chains and pulleys above a gateway | Gate to a city, blocks off portions of sewers, etc. | Manual or broken mechanism | Perception 10 to notice | Portcullis closes | Wedge the portcullis open, jam the gears, disable operator | Trapped, possibly falls on a person for 1d6 bludgeoning damage |
| 1/8 | Hidden Net | A net is hidden above, while a tripwire is hidden in tall grass | Someone is looking for their next meal, guarding their home, or ambushing the adventuring party | Walking through the tripwire | Perception 10 to notice | Net falls over 10×10 area | Cut net; trigger harmlessly with a thrown dagger (wire AC 10) | Restrained |
| 1/4 | Hidden Crossbow | Crossbow is hidden in a nook of a tree | Kobolds waiting to ambush victims, bandits discouraging people from following them, slow someone down | Tripwire | Perception 12 to notice | Bolt fires at whomever tripped the wire | Remove tripwire, remove crossbow from tree | 1D6 piercing damage unless victim has AC higher than 18 |
| 1/4 | Hidden Pit | A pit in the ground, deep, hidden by a camouflaged covering | Trap or injure creatures and people | Step on cover | Perception 12 to notice | Fall 10 feet | Walk around, uncover tarp, mark the area | Fall damage, injury, trapped |
| 1/2 | Rolling Rock | Boulder ready to roll! | Kill grave robbers in bulk | Tripwire/ pressure plate | Perception 12 to notice | Crushed or knocked aside | Avoid or trip it harmlessly | 3d8 bludgeoning damage halved by a strength saving throw (DC 10) |
| 1/2 | Dart | Darts spring-loaded in many holes | Injure and frighten dungeon looters | Tripwire/ pressure plate | Perception 12 to notice | Darts fire at whomever tripped the trap | Avoid or trip it harmlessly | 2d4 piercing damage halved by a dexterity saving throw (DC 10) |
| 1 | Scything Blade | Blade spring-loaded behind a door | Kill intruders in a lair | Open a door | Perception 12 to notice | Blade swing at door opener | Avoid or trip it harmlessly. Unhook a spring so it swing into door before opening. | 1d12 slashing damage halved by a dexterity saving throw (DC 10) |
| 1 | Flashbang | Explosion of blinding light and deafening sound | Disorient intruders while guards arrive | Turn a key in a lock | Perception 12 to notice | Senses bombarded | Pour water on the keyhole | Deafened and blinded for three rounds unless passing a constitution saving throw (DC 10) |
| 1 | Rabies rat | Rabid rodent waiting to bite | Pass disease to a greedy thief | Try a door handle | Perception 12 to notice | Leashed rat pounces to bite hand | Plug the hole | 1d4 piercing damage, and constitution saving throw to avoid the poisoned condition for one week (DC 10) |
| 1 | Swinging Blade | Many pendulum blades constantly swinging | Allow a capable few to continue | Always going | Perception 12 to notice | Cut to pieces and fall | Use rope to tie around all swinging blades. Be creative. Jump through. | 1d12 slashing damage any time an acrobatics or athletics check of 8 is failed to jump passed each blade |
| 2 | Falling Rocks | Rocks secured above in a net | Kill guards and seal a passage | Tripwire/ pressure plate | Perception 12 to notice | Crushed, trapped, or blocked | Avoid or trip it harmlessly. Move tripwire to a support beam. | 2d8 bludgeoning damage halved by a dexterity saving throw (DC 11) |
| 2 | Mischief Monkey | Kleptomaniac monkey kifes goods through hand-sized holes in a wall | Disarm intruders and add their treasures to a hoard | Walk by | Perception 12 to notice | Stuff stolen by monkey | Plug holes. Kill monkey. Cut off monkey’s hands. Go naked. | Stuff stolen unless noticing the monkey. DM decides what stuff |
| 2 | Poison Needles | Poisonous darts spring-loaded in many holes | Kill pyramid robbers who would defile the tombs | Tripwire/ pressure plate | Perception 12 to notice | Darts fire at whomever tripped the trap | Avoid or trip it harmlessly | 1d4 piercing damage and 1d8 poison damage halved by a constitution saving throw (DC 11) |
| 2 | Spiked Pit | A pit in the ground with spikes, hidden by a camouflaged covering | Capture and injure a feral beast that plagues the town | Step on cover | Perception 12 to notice | Fall 10 feet | Walk around, uncover tarp, mark the area | 4d4 piercing damage |
| 3 | Fire Trap | Subtle oils coat the walls and a spark is all it needs | Roast investigators and incinerate secret research | Open a drawer that has flint and steel built in | Perception 12 to notice | Research burned to ashes, people burned | Pour water over the desk or open drawer slowly | 1d8 fire damage per round unless getting out of the room fire and putting flames out on self with an action. |
| 5 | Collapsing Column | Ceiling built to lower to five feet | Dwarven trap to make tall people crouch in battle | Pull a lever | Perception 13 to notice | Tall people must crouch | Pull lever again. Machinist tamper with gear.s | Crouch and move as difficult terrain, melee attacks disadvantage while crouching here. |
| 5 | Flooding Room | Water ready to flood the room | Drown intruders and wash their bodies out of the sacred temple | Pressure plate | Perception 13 to notice | Room flooded within five rounds | Avoid trigger, or adapt to water (Water Breathing spell) | See suffocation rules in PHB |
| 6 | Contact Poison | Treasure chest coated in touch-activated poison | Kill greedy thieves and then keep their stuff | Touch a treasure chest | Perception 13 to notice | Toucher is poisoned | Use gloves that you can wash or dispose of. Or rinse treasure chest in oil. Gain immunity to poison. | 4d12 poison damage halved by constitution saving throw (DC 14) |
| 10 | Shrinking Room | All walls built to close in and crush | Kill all who intrude in thieves guild | Tripwire/ pressure plate | Perception 15 to notice | Room crushes all inhabitants within five rounds | Avoid trigger | Crushed to death. Body destroyed. |
| 10 | Insanity Mist Trap | Alchemist gas in breakable flask | Alchemist sets a trap for any who would steal his research | Unravel a scroll and drop flask | Perception 15 to notice | All who breathe the mist must attack the person closest to them for three rounds | Unravel scroll on a table rather than holding it up. Otherwise find a way to not break the flask. | Attack the closest person for three rounds unless passing a wisdom saving throw (DC 16) |
| 15 | Rail Gun | Large rod set to launch with great force | Necromancer took a dinosaur bone and made it a spring-loaded weapon to blast through any who would discover his mausoleum of underoath | Pressure plate/rung built into a ladder | Perception 18 to notice | Rail shoots through whomever is using the ladder | Use rope to trigger harmlessly, or avoid triggering until removing the bolt | 50 bludgeoning damage to anyone climbing the ladder. Fall down the ladder unless passing a strength saving throw (DC 18). |
Other Trap Resources
If you want more information and ideas about traps (and especially puzzles), check out Wally DM’s puzzle and trap resources on his site. He has a best-selling puzzle book on the DM’s Guild, so he’s a fantastic resource for these sorts of things.
