For that upcoming Tribality project that I’ve mentioned, I’m writing traps based on gunpowder and firearms for use in D&D 5e. Er, without just making a numbers-bolted-on collection of gunpowder bombs and land mines, I guess. If you want those for your game, that’s fine, but you can read the Damage Severity by Level table just as well as I can.

Flashplate

Simple trap, level 1-4 (moderate threat)

This trap is a layer of black powder between two layers of cotton, placed inside a chest or safe. A flint striker is attached to the locking mechanism; if someone attempts to open the lock without also pressing a button or using a key that interferes with the striker, the flashplate catches fire. Harming a thief is a secondary consideration to destroying any documents or other flammable, sensitive goods stored in the container.

Trigger. A creature that opens the container triggers the trap.

Effect. The creature makes a DC 12 Dexterity saving throw. On a success, they can either save items in the chest from being incinerated (taking damage as if they failed the saving throw), or they can take no damage from the trap (and items in the chest burn to ashes in moments). On a failure, they take 2d6 fire damage and the items in the container are destroyed.

Countermeasures. A successful DC 12 Wisdom (Perception) check detects the flint striker in the lock, and a successful DC 12 Dexterity (thieves’ tools) check blocks the striker’s movement. Alternately, a DC 15 Wisdom (Perception) check detects a catch in the container’s door or lid; pressing this catch disables the striker and allows the container to be opened safely.

Petard Door Trap

Simple trap, level 5-10 (dangerous threat)

A petard is an early form of shaped charge, used in siege warfare and breaching doors or thin walls. The petard weighs 25 lb. and is portable and deployable with 1 minute of effort by a skilled user; running twine or a chain to a closed door makes a petard door trap. Triggering the trap sets off an explosion that blows the door apart, potentially injuring anyone on the other side. The trap is set differently depending on which way the door opens, but the effect is the same.

Trigger. A creature that opens the door from the other side triggers the trap.

Effect. The door explodes, and creatures on that side of the door and within 10 feet of it make a DC 15 Dexterity saving throw. A creature that fails this saving throw takes 4d10 fire damage and is blinded and deafened for 1 minute. A creature that succeeds takes half damage and is not blinded or deafened. The explosion emits a boom audible out to 300 feet.

Countermeasures. A creature that looks through the door (through a keyhole, through a window in the door, or the like) automatically detects the petard. Knocking or tapping at the door can detect the presence of something unusual with a DC 15 Wisdom (Perception) check.

Detonating the petard door trap while no one is in its 10-foot area of effect is the most direct solution. Otherwise, a character can cut the twine or break the chain connecting the trap to the door with a DC 15 Dexterity (thieves’ tools) check. Knocking the petard door trap down so that it isn’t placed against the door makes it explode, but halves the damage that it deals and expands its area of effect to include creatures within 10 feet of it on the other side of the door.

Blast Sphere Launcher

Complex trap, level 5-10 (deadly threat)

This marvel of construction and destruction is usually placed in an interior chamber, to protect it from interference by enemy creatures, but it can be used outdoors as well if hidden or assigned some screening defenders. The blast sphere launcher launches bombs on a short fuse, which deal damage to nearby creatures. It can be used to delay and scatter an advancing force, or during combat if the defenders are flying or resistant or immune to fire and thunder damage.

Trigger. This trap activates when a creature within 5 feet of the launcher turns it on with a successful DC 10 Intelligence (Investigation) check, or when a creature steps on a large pressure plate that is between 100 and 180 feet from the launcher.

Initiative. The trap acts on initiative count 20 and initiative count 10.

Active Elements. The Blast Sphere Launcher includes a launcher cannon that fires incendiary rounds at targets more than 60 feet away, concussive rounds at targets more than 30 and less than 60 feet away, and lengths of chain at targets closer than 30 feet. It fires once on initiative count 20 and once on initiative count 10. When there are enemy creatures in more than one of these ranges, the Blast Sphere Launcher fires at the nearest range that has an enemy in it.

Incendiary Rounds. The Blast Sphere Launcher fires two metal spheres filled alchemist’s fire. One lands in an empty space within 5 feet of a random enemy creature; the other lands 15 feet away from all creatures. The spheres are Tiny objects weighing 15 lb. They are superheated as they count down toward explosion, and a creature that touches them takes 3 (1d6) fire damage. On the next initiative count that matches the one on which they were fired, they explode. Creatures within 10 feet of a sphere roll a DC 15 Dexterity saving throw, taking 16 (3d10) fire damage on a failure, or half damage on a success. The ground in that area is set on fire for 1 minute, and a creature starting its turn in that effect area takes 5 (1d10) fire damage.

Concussive Rounds. The Blast Sphere Launcher fires two metal spheres resonating with thunderous energy. One lands in an empty space within 5 feet of a random enemy creature; the other lands 15 feet away from all creatures. The spheres are Tiny objects weighing 15 lb. On the Blast Sphere Launcher’s next initiative count, they explode; they also explode immediately if touched. Creatures within 10 feet of a sphere roll a DC 15 Strength saving throw. A creature that fails this saving throw takes 16 (3d10) thunder damage and is pushed 10 feet away and knocked prone; a creature that succeeds takes half damage and no further effect.

Chain Shot. The Blast Sphere Launcher fires a length of chain. Creatures in a 30-ft cone from the launcher roll a DC 15 Dexterity saving throw. A creature that fails this saving throw takes 18 (4d8) bludgeoning damage and is restrained until the end of their next turn. A creature that succeeds takes half damage and is not restrained.

Dynamic Elements. The dynamic aspect of the Blast Sphere Launcher is that Concussive Rounds and Chain Shot become an active part of combat as the character get closer to the launcher itself, and the available reaction time for each shot is shorter than the shot before it.

Countermeasures. The primary countermeasure is moving away from incendiary and concussive rounds before they explode, or moving the spheres. A creature within 5 feet of the launcher can use their action to make a Dexterity (thieves’ tools) or Intelligence (Investigation) check against DC 20. On a success, the launcher loses the use of one of its Active Elements.

The Blast Sphere Launcher is often protected by a walls of stone or brick that grant it three-quarters cover. It is an object with 150 hit points, an AC of 15, and immunity to poison and psychic damage.

Design Notes

The concept-level issue I ran into was just coming up with specific applications that made the traps more than a lookup on the Trap Save DCs and Attack Bonuses table and the Damage Severity by Level table. Document security is a pretty niche use in some settings, more common in others, but I stand by it.

The Petard Door Trap is 95% real – the only meaningful change is wiring it to the door to make it a trap, rather than a breaching charge used to take down a sturdy door. If you’re familiar with the Shakespearean phrase “hoist by [their] own petard,” this is the device. I’ve played down the danger to the user, because we also play down the danger of flintlock misfires.

The Blast Sphere Launcher is inspired by a bunch of different MMO boss fights, and I’m not sorry. The main thing I see as a potential problem with it, as a complex trap design, is that maybe it doesn’t have a sufficiently dynamic nature? I don’t know. Maybe it behaves too much like a sessile construct. The challenge – not to say problem – in running it is remembering when incendiaries and concussives should explode, because there is a time delay. I’d recommend using d6s: set incendiaries to 2 and concussives to 1, and tick them down a face at the start of the BSL’s turn. They go big badaboom when they would tick down to 0.

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