The Chaos Engine
A Trap Encounter for DnD 5e
Water. Earth. Fire. Air.
What powers and activates all those magical traps and moving parts in your fancy mage dungeon? This encounter attempts to answer that, while also making an engaging trap and combat for your player characters. This is a deadly encounter for a group of player characters around 5th to 7th level.
The Trap
Confined Space: The 5 foot diameter chaos engine is suspended in the center of a 40-foot diameter room of smooth scorched stone. The top is connected to the ceiling and the bottom connected to the floor by intricate lines of adamantine pipes and gears. Four distinct semi hemispheres make up its spherical form.
Trigger: While the party is in the engine room, the doors close as an alarm rings. The engine begins whirring. Roll initiative!
This is a trap, but it is not meant for the player characters. The engine closes the doors and powers up whenever undead get close to the engine room. But none of the party members are undead! Not to worry the undead will be revealed in time.
Harm: On initiative count 20, roll 1d4. The four semi hemispheres of chaos rotate clockwise a number of positions equal to the roll. For example, if the air element was pointed north, and a 3 was rolled, it would rotate clockwise to point west instead, with all the other elements rotating to accommodate the change as well.
On initiative count 10, each semi hemisphere of the engine releases a blast of elemental energy outward in a 20-foot cone, whose origin is the center of the chaos engine sphere. All four blasts combined covers the room in its entirety, though they should not overlap, nor effect the adamantine structures suspending the sphere. See "Semi Hemisphere Hazards" for more information.
Art - The Orb
Trey Ratcliff
Semi Hemisphere Hazards
Water hemisphere
- Each creature in the 20 foot cone must make DC 13 Dexterity saving throw.
- On a failure, the target takes 2d8 cold damage and is chilled until the start of its next turn. A chilled creature cannot take reactions. The chilled effect ends early if the target takes fire damage.
- On a success, the target takes half damage and is not chilled.
Earth hemisphere
- Each creature in the 20 foot cone must make DC 13 Constitution saving throw.
- On a failure, the target takes 2d10 thunder damage and is deafened until the start of its next turn.
- On a success, the target takes half damage and is not deafened.
Fire hemisphere
- Each creature in the 20 foot cone must make DC 13 Constitution saving throw.
- On a failure, the target takes 2d8 fire damage and catches fire. While on fire, the target takes 1d4 fire damage at the start of each of its turns. Someone, including the target can take an action to douse the fire. The fire also extinguishes if the target takes cold damage.
- On a success, the target takes half damage and does not catch on fire.
Air hemisphere
- Each creature in the 20 foot cone must make DC 13 Strength saving throw.
- On a failure, the target takes 2d6 force damage and is pushed 15 feet away from the sphere. If the target collides with a wall or object due to this movement, it takes 1d6 bludgeoning damage. If the target collides with a creature, both the target and the creature take 1d6 bludgeoning damage.
- On a success, the target takes half damage and is not moved.
Chaos Engine Rotation Direction
Art - Engine GreenDM
Semi Hemisphere Boons
The sphere is not all bad news. If a creature touches one of the hemispheres, which requires no action, the magic of the hemisphere envelops them for a moment.
Water hemisphere
- Until the start of the target's next turn, it is soaked in water.
- While soaked, the first time the target is dealt fire damage, it instead takes no fire damage and it becomes no longer soaked.
Earth hemisphere
- Until the start of the target's next turn, it is encased in rock.
- While encased, the target's speed is halved.
- While encased, the target gains a +2 bonus to AC.
- While encased, the target has resistance to bludgeoning, piercing and slashing damage.
Fire hemisphere
- Until the start of the target's next turn, fire swirls around it.
- While this fire swirls, the target is resistant to cold damage, if it was not already.
- While this fire swirls, creatures that hit the target with a melee attack take 1d8 fire damage.
Air hemisphere
- Until the start of the target's next turn, air swirls around it.
- While the air swirls around it, the target gains a flying speed equal to its walking speed.
- While the air swirls around it, the target does not provoke attacks of opportunity.
You spin me right round
With both the boons and hazards, and the rotating nature of the trap, your player characters should be continually on the move. Whether that is to avoid a particular elemental blast they believe is deadly, or follow the one hemisphere they can withstand the damage from is up to them.
However, just running around is going to get boring and most likely very taxing on their health. So how are they going to get out of here? Well players of course can always surprise you, but there are two options built into the encounter. One is the monsters that triggered the engine's defenses in the first place and the other is the engine's destruction.
Enjoy!
From the Green DM
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Twitter: @YTGreenDM
A surprise threat
On the second round the player characters are trapped within the engine room, a 10 foot cube of wall disintegrates as a beholder zombie (MM 316) floats into the room. Behind it is two ogre zombies (MM 317).
This is the reason the engine room went on lock down and began spinning. Why these powerful zombies are trying to break into the heart of this dungeon is up to you, but in my game it was caused by a war between an aboleth (MM 13) and an necromancer alhoon (VGM 172), with the aboleth having enslaved the alhoon's minions and sent them back at it. With the dungeon being one of the alhoon's liars. No matter the reason, the player characters are seen as threats by the zombies and are immediately attacked.
The initiative of the zombies can be rolled, or simply placed at initiative count 15, losing ties, so that it is right between the two chaos engine actions.
The zombies are too dumb to try to position themselves strategically around the room or extinguish flames burning on them. Smart players may be able to get the zombies to stand in the fire cone and then burn for the rest of the encounter.
Once all the zombies are destroyed, the engine will shut off and go back to its dormant state, opening the room's doors.
GET DOWN MR. PRESIDENT!
Beholder zombies are incredibly dangerous, especially if they use their disintegrate ray. Failing the save against it could mean a player character is killed instantly. If possible I recommend having a few NPCs come with the players on this adventure, so one can bite the bullet if the beholder uses that ray during combat. Or I recommend not using that ray during combat, or it does less damage.. Perhaps that ray cannot be used for a while after blowing through the wall.
Just shoot the damn thing!
Players that want to destroy the engine before it spews more elemental damage may do so by targeting the adamantine structure holding it in place. The ceiling connection and floor connection both have an AC of 23, 20 HP, and a damage threshold of 5, which means if either takes less than 5 damage from a single attack or effect, it instead takes 0 damage.
Both the top and bottom connections must be severed for the engine to stop entirely, but if one connection is severed, the engine will be less dangerous. It will rotate one position each round, instead of 1d4 positions. The elemental hazards will only do one die of damage and will not have their secondary effects, such as chilled and deafened.
When both connections are severed, the engine will immediately emit a burst of elemental energy. This burst does the normal two dice of damage from each hazard in a cone, but also provides those standing in each cone that respective hemisphere's boon. The sphere then falls and lies dormant, opening the doors to the room.