The Fourfold Run | Fantasy Hazard Generated by CharGen

The hazard

The party escapes the collapsing chamber and hurries into a long hallway. Dust sifts from the ceiling, grit crunches underfoot, and a faint metallic tang clings to the air. A step lands on a sunken stone plate. Copper seams flare, and a rushing elemental force begins to race through the corridor.

Magical
Complex
Elemental
Pressure Plate

Stealth: The pressure plate is hidden among worn floorstones. A creature that moves at a normal pace has a chance to notice it with the listed Perception check. Dust from the collapsing room can obscure the plate, imposing disadvantage on that check if the party is moving hurriedly.
Trigger: A creature weighing at least 20 pounds steps on the pressure plate near the corridor entrance.
Disable: A creature adjacent to the plate can use an action and thieves' tools or a suitable implement to make a Dexterity check, wedging the plate on a success. Alternatively, a creature adjacent to a copper seam can use an action to make a Intelligence (Arcana) check. Three successful checks disable the conduit; each failed check triggers the current pulse immediately. Destroying the mechanism also disables the hazard.
Initiative: The hazard acts on initiative count 20, losing ties. It begins acting immediately after its trigger.
Routine: On initiative count 20, the hazard releases one pulse in this repeating order: Wind, Flame, Stone, Water. It affects creatures in the corridor that are not behind full cover. The sequence advances even if no creatures are present.
Reset: After the Water pulse, the sequence returns to Wind on the next initiative count 20. The hazard continues cycling until disabled or destroyed.

Damage

Immunities

Poison damage, Psychic damage

Weaknesses

A successful DC 15 Intelligence (Arcana) check made as an action can identify the conduit carrying the next pulse, granting advantage on the next saving throw against that pulse to one creature the checker can see.
A creature in an alcove is protected from all four pulses while it remains there.

Effects

1

Elemental Pulse
DC 15
On initiative count 20, the corridor releases the next pulse in its sequence. Each creature in the corridor that is not behind full cover makes the listed saving throw. Wind: Strength saving throw or be pushed 15 feet toward the far end and knocked prone. Flame: Dexterity saving throw, taking fire damage on a failure, or half as much on a success. Stone: Dexterity saving throw, taking bludgeoning damage and becoming restrained until the end of its next turn on a failure; on a success, take half damage and avoid being restrained. Water: Constitution saving throw, taking cold damage and having speed reduced to 0 until the end of its next turn on a failure, or half damage on a success with no speed reduction.

Special rules

Sheltering Alcoves.The corridor's wall alcoves provide full cover from the elemental pulses. Each alcove can shelter one Medium creature or two Small creatures.

Awakened Sequence.The initial plate trigger begins the sequence immediately. The hazard then acts on initiative count 20. Stepping on the plate again does not restart or alter the sequence.

Spotting it

Discovery

A Wisdom (Perception) check reveals the pressure plate before it is stepped on.

Perception

Wisdom (Perception) to notice the pressure plate before triggering it.

Stop it

Signs of dangerCopper seams glimmer briefly beneath the dust. · The wall alcoves are cleaner than the surrounding stone, as if they have offered shelter before. · The air carries alternating scents of scorched metal and wet stone.

Countermeasures

DC 15A creature that succeeds on a Wisdom (Perception) check notices the recessed pressure plate before stepping on it. A Intelligence (Investigation) check identifies the copper seams as part of the same mechanism.
DC 15A creature adjacent to the plate can use an action to wedge it with a sturdy object, succeeding on a Dexterity check using thieves' tools or a suitable implement. On a failure, the plate triggers.
DC 15A creature adjacent to a copper seam can use an action to disrupt the conduit with a Intelligence (Arcana) check. Three successes disable the hazard. A failed check causes the current pulse to erupt immediately.
The stone mechanism can be broken. It has AC 17 and 45 hit points, and it is immune to poison and psychic damage. Destroying it disables the hazard.
The wall alcoves provide full cover from the corridor's elemental pulses. A creature can reach an alcove by spending 5 feet of movement.

In short

Find and disable the pressure plate or the elemental conduit, take cover in the wall alcoves, or time a crossing between pulses.

Its story

What it looks like

A 60-foot corridor of dark basalt, divided into four 15-foot stretches.

Why it is here

To stop intruders escaping the ruin's inner chamber.

Who made it

An unknown elemental engineer, likely working for the ruin's former keepers.

Lore

The corridor was built to punish intruders who fled the chamber beyond it.

Where it is found

Ruins

Variants

Ashen Sequence: Replace the Water pulse with a cloud of choking ash. Creatures in the corridor make a DC 15 Constitution saving throw, taking 3d8 poison damage on a failure or half as much on a success.

Unstable Conduit: After each full four-pulse cycle, roll a d4. On a 1, the next pulse erupts twice, with each creature affected making its saving throw separately.

Keeper's Passage: One alcove contains a hidden rune. A creature that uses an action to touch it and succeeds on a DC 15 Intelligence (Arcana) check can safely cross until the end of its next turn.

Plot hooks

The elemental conduit is keyed to a seal deeper in the ruins. Disabling the hallway may also weaken the ward protecting that seal.

A surviving attendant knows the pulse sequence but refuses to enter the corridor until the party promises to recover a lost component.

The pressure plate is still active after the party passes. Something pursuing them may trigger it behind them.

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