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Brass Pendulum Gate - AI-generated fantasy Hazard

Brass Pendulum Gate

The Brass Pendulum Gate is a clockwork security device that sweeps a hidden blade and launches a burst of metal timing pins across a marked section of floor. It rewards patience and observation, but punishes anyone who treats its ticking as background noise. The hazard is simple to run, yet its visible timing cycle gives characters meaningful table-facing counterplay.

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Hazard EntryMechanicalLevel6Simple

Brass Pendulum Gate

6LevelUncommonRarityDungeonEnvironment
MechanicalClockworkAudibleArea HazardTimed
Level6
|
HP30
|
AC15
|
TypeMechanical
|
ComplexitySimple
|
RarityUncommon

Defenses

AC15
HardNot applicable in D&D 5E. The housing has resistance to bludgeoning, piercing, and slashing damage from nonmagical attacks.
HP30
BT 8
Fort+Not applicable in D&D 5E. The housing has AC 15 and 30 hit points.
Ref+DC 15 Dexterity saving throw when triggered
Will+Not applicable in D&D 5E. The hazard has no mental defenses.
Immune
Poison damage, Psychic damage, The poisoned condition, The charmed condition
Resist
Bludgeoning, piercing, and slashing damage from nonmagical attacks
Weak
A successful DC 15 Dexterity check with thieves' tools can lock the timing wheel., A sturdy object can jam the main gear with a successful DC 16 Strength (Athletics) check., The mechanism is vulnerable to careful manipulation of its exposed timing cog.
MechanicalClockworkAudibleArea HazardTimed

Detection

PerDC 14 Wisdom (Perception) to notice the concealed housing and floor track before triggering the hazard. The ticking can be heard through a closed door with a successful DC 12 Wisdom (Perception) check.
StlDC 14 to notice the concealed mechanism before it triggers
InitThe hazard acts immediately when triggered. It has no initiative count before activation.

“A waist-high brass housing is set into the dungeon wall, its face crowded with numbered apertures and rotating toothed rings. A narrow track runs across the floor in front of it. The mechanism ticks softly, though the rhythm changes whenever a creature approaches.”

Standard Engagement

Trigger

The hazard triggers when a creature crosses the marked floor track, tampers with the brass wall panel, or moves the timing rings without first disabling the mechanism.

Routine

The mechanism emits three quick ticks, pauses, and then releases a concealed crescent blade across the marked track while launching metal timing pins from the wall. The sweep lasts for an instant, after which the blade retracts and the mechanism begins resetting.

Reset

The hazard resets after 1 minute as the blade retracts and the timing rings realign. If its housing is destroyed or its timing wheel is jammed, it does not reset.

Razor Sweep

When the hazard triggers, each creature in the 20-foot-long, 5-foot-wide track must make a DC 15 Dexterity saving throw. On a failed save, a creature takes 4d8 slashing damage and is knocked prone. On a successful save, it takes half as much damage and is not knocked prone.

Locking Teeth

A creature that fails the saving throw by 5 or more is caught by the locking teeth. Its speed becomes 0 until the end of its next turn, and it cannot take reactions during that time.

Marked Track

The hazard's firing area is clearly marked by a 20-foot-long, 5-foot-wide strip of unusually clean stone. A creature can avoid the hazard entirely by remaining outside this area when it triggers.

Audible Cycle

The device gives an audible warning before firing: three quick ticks followed by a low chime. A creature that can hear the warning and is not surprised can use its reaction to move up to 5 feet without provoking opportunity attacks, potentially leaving the firing area.

Description

The Brass Pendulum Gate is a clockwork security device that sweeps a hidden blade and launches a burst of metal timing pins across a marked section of floor. It rewards patience and observation, but punishes anyone who treats its ticking as background noise. The hazard is simple to run, yet its visible timing cycle gives characters meaningful table-facing counterplay.

Discovery

The hazard is noticed when a creature enters the dungeon corridor. It is concealed behind a decorative brass panel, but the panel and floor track are visible with a successful DC 14 Wisdom (Perception) check. A character who examines the area without pressure automatically notices the track, though not the firing mechanism.

Archival Lore

“The device was built to guard a vault where the order stored precision instruments, forbidden automata, and a mechanical calendar said to predict eclipses. Its makers designed the rhythm to be learned, not guessed. Ancient maintenance marks near the housing show that at least one former intruder survived by listening rather than fighting.”

Environment
Dungeon
Theme
Clockwork
Creator
The horologist-priests of Veyr, an extinct order that believed perfect mechanisms could reveal the will of fate
Purpose
To prevent unauthorized creatures from crossing into a clockwork vault or maintenance corridor
Game System
D&D 5E
Art Style
Dark fantasy dungeon machinery, tarnished brass, black iron, ruby indicator lights, harsh directional shadows, intricate clockwork detail
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