Chamber of Cinders
Complexity: Complex (multi-round encounter with recurring actions and escalation)
Type: Hybrid — mechanical (pressure plate, valves, oil/gas lines) + magical (bound fire rune under medallion)
Severity: Dangerous (designed for Average Character Level ~7). — Scaling: reduce dice for lower levels or increase for Deadly encounters.
Trigger: Primary: Subtle pressure plate under the central five-foot corridor mosaic. Any step applying ≥10 lb to the central five feet except the center medallion triggers the mechanical system. Secondary: Magical rune beneath the medallion that senses sudden movement/heat and will activate (or re-activate) the trap if mechanical safeguards fail.
Effect: When triggered the trap fires synchronized jets of ignited oil/gas across three 20-foot lines in the corridor, flares the rune (increasing damage and creating lingering embers), fills the chamber with thick smoke, and—if left active—softens hidden supports so a section of floor collapses on round 3 and the rune may erupt into an even deadlier arc of radiant-tinged flame.
Damage Output: Sweeping jets of burning oil/gas + magical flare; hits creatures in chosen 20-foot lanes. (Fire (primary); radiant+fire (rune eruption))
Detection DC: Passive Perception: 13 will notice warmth or faint burnt smell. Active Perception DC 13: Notices slightly raised tiles, hairline seams, faint warmth, or a sulfur smell. Investigation DC 15: Discerns the false tile/pressure plate seam, traces soot deposits to hidden nozzles, finds an access seam under a loose tile. Arcana DC 14: Detects magical residue and recognizes a bound fire rune beneath the medallion. Detect Magic: reveals a faintly flaming aura centered on the medallion.
Disarm DC: Disarm Difficulty (primary methods): Mechanical Jam (Thieves’ Tools): Investigation DC 15 to locate access seam/panel under the identified tile. Thieves’ Tools (Dexterity check with tools) DC 15 to jam the pressure plate and lock the brass valves. Failure: immediate partial trigger — half the jets fire (half listed damage). Failing the check by 5+ causes a spark/partial blast that damages the disarmer (GM rolls half-trigger damage to disarmer). Magical Suppression: Arcana DC 15 to identify rune function and the 3-round timing window; success reveals rune is tied to an earth-node (can be disrupted). Casting Dispel Magic: treating rune as a 3rd-level continuous effect suppresses it for 1 hour. If the GM treats it as >3rd-level, require a caster spellcasting ability check (DC = 10 + rune’s effective level; GM default DC 14 for a 4th-level equivalent). Alternate: Arcana DC 15 to redraw a counter-stroke (requires an action and artisan’s tools) to mute rune for 10 minutes; failure risks an immediate 3d8 fire flare with Dex save DC 14 for half. Improvised Bypass: Leap the mosaic (Athletics DC 12) or use poles to apply pressure from distance; success bypasses jets. Water applied to nozzles can reduce effect (improvised check DC 12). Combat Disarm: A character can use an Action during the trap’s encounter rounds to attempt disarm checks above. Successful mechanical jam stops jets and prevents floor collapse; successful magical suppression mutes rune and prevents eruption.
The corridor’s floor is a dazzling mosaic of tiles forming a sunburst; the central medallion is slightly raised and etched with tiny glyphs that glow like coals when you draw near. At first glance the chamber is an architectural hymn to heat: brass piping runs in neat grooves along the base of the wall, bronze nozzles sit flush like capped teeth, and the grout between tiles is stained black with soot. When the air is still, a faint sulfur tang clings to the tiles and a subtle warmth rises from one quadrant of the mosaic. If someone steps on the wrong tile, bronze valves hiss open beneath the floor and a synchronized column of flame erupts in sweeping ribbons across chosen lanes, throwing back faces with searing heat and spitting smoking embers that cling to hair and mail. The rune beneath the medallion chirrups in time with the jets, tinting the flames with a blinding, radiant edge. Smoke pours up and blankets the center of the corridor, and if the fire runs long enough, hidden clay supports beneath a portion of the floor give way—bringing the unwary down into spikes and broken stone. The whole scene is theatrical: the sun-eye medallion pulses, the nozzles gleam, and the baked stone smells of oil and old ritual. Players who notice the hairline seams, feel the warmth under tiles, or sense the rune’s faint magical heat can choose to pry a tile, jam a ratchet, or mute the sigil with arcane skill—each method carrying risk if botched but rewarding if done cleanly.
Below are ready-to-run gameplay notes to help you run the Chamber of Cinders smoothly at the table. They explain exactly how the trap activates, what the players can detect and do, how it behaves across multiple rounds, suggested variations/tactics, and practical tips for tracking the trap’s effects.
Quick refresher (core stats)
- Trigger: Hidden mosaic pressure plate (central 5-foot corridor tiles except medallion); 10+ lb. Secondary trigger: magical rune under central medallion that senses heat/motion.
- Detection DCs: Perception DC 13, Investigation DC 15, Arcana DC 14.
- Disarm: Thieves’ Tools (Dex + thieves’ tools) DC 15 to jam mechanics; Arcana DC 15 to locate/suppress rune; Dispel Magic (3rd level or higher) to suppress rune (see below).
- Initial damage (level 7 Dangerous): 6d10 fire (Dex save DC 14 for half).
- Ongoing embers: 2d6 fire at start of affected creature’s turn for up to 2 rounds unless extinguished.
- Floor collapse (if rune still active after 3 rounds): 15-foot fall into pit or 4d10 bludgeoning (Dex save DC 14 for half) and possible prone.
- Rune eruption (if not suppressed by 3rd round): 4d10 radiant+fire; Wisdom save DC 14 to avoid being stunned until end of your next turn.
For all traps — Activation, detection, and disarm notes
Trap Activation (when it starts)
- Primary mechanical: Any creature applying 10+ lb of pressure to one of the central five feet of the mosaic (any of the tiles in the main corridor except the central medallion) immediately depresses the pressure plate and starts the trap sequence.
- Secondary magical: If mechanical activation fails, the rune beneath the medallion will trigger on a sudden change of heat or rapid movement in the medallion’s space (for example, someone touching or slamming the medallion, or large bursts of magic or fire nearby).
- Immediate effect at trigger: The oil/gas nozzles fire their initial jets immediately when the trap is triggered (see Round 1 effects below). After the immediate firing, roll initiative for the trap to handle subsequent rounds of activity.
Detection and Disarm Notes (before activation)
- Clues (flavor + play cues): hairline seams in the mosaic, faint warmth from one seam, soot-stained grout, faint sulfur smell, subtle creak of hidden bronze valves, faint pulse visible with Detect Magic on the medallion.
- Spotting checks:
- Perception DC 13 (passive Perception 13+ will notice warmth/smell if paying attention).
- Investigation DC 15 to find the exact raised tile, access panel beneath the tile, and gas lines/nozzles.
- Arcana DC 14 to recognize the rune’s presence and infer its function.
- Disarm approaches (pre-trigger and mid-sequence):
- Mechanical jam: Investigation DC 15 to locate access and Thieves’ Tools (Dex + thieves’ tools) check DC 15 to jam the pressure plate and lock valves. Success disables the mechanical system permanently. Failure: immediate minor reaction (see failure consequences).
- Magical suppression: Arcana DC 15 to understand the rune’s linkage and timing. Casting Dispel Magic (3rd level or otherwise) on the rune suppresses it (treat tile/rune as a 3rd-level or GM-determined continuous effect — if higher, require a spellcasting check vs DC 14). A successful Arcana DC 15 (redraw counter-stroke) mutes the rune for 10 minutes but fails may cause a flare (see failures).
- Bypass: Leap across a 10-foot gap, use an alcove/side path, or depress tiles remotely with poles. Water applied to nozzles reduces effectiveness (improvised check DC 12).
- Disarming in combat / mid-sequence:
- A disarm attempt requires an action (or an action + thieves’ tools/Arcana check). If the mechanical is jammed before the third round, no floor collapse will occur. If the rune is dispelled or suppressed before the third round, the rune eruption won’t happen.
Consequences for failed disarms
- Thieves’ Tools failure by 5 or more: immediate partial discharge — half the jets fire immediately, dealing half the listed initial damage; the mechanism remains active and may fire again next round.
- Arcana redraw failure by 5 or more: rune flares — affected character makes Wisdom save DC 14 or is stunned 1 round and takes 3d8 fire immediately.
- No disarm in 3 rounds: trap fully escalates: floor collapse + rune eruption (if rune still active).
Complex trap section — how to run it round-by-round
Initiative rules and immediate effect
- Immediate firing: When a creature triggers the trap by stepping on the plate, the jets fire immediately (apply initial jet damage and embers). After applying that immediate effect, roll initiative for the trap and for the PCs (if you have not already rolled). This gives the trap an immediate “first strike” followed by its normal initiative in subsequent rounds.
- Trap initiative modifier: +1 suggested. Alternatively, have the trap act immediately on the triggering turn and then act on initiative count 10 (or whatever is easiest); using +1 is simpler for consistent behavior.
- The trap acts as its own combatant and uses its turn each round to change jet lanes, increase smoke, or trigger the floor collapse and rune eruption.
Mapping and lane setup
- When you prepare the map, choose three 20-foot jet lines that the jets will fire across. Common layout options:
- Center corridor + two flanking lanes.
- Staggered lanes covering likely movement routes.
- Mark these lanes with tokens or penciled lines so you can change which lanes are active each round.
Round-by-round effects and trap actions
Round 0 — Trigger (immediate effect)
- Initial jets: Bronze nozzles fire oil/gas jets across the three preselected 20-ft lines. Every creature in a line must make a Dexterity saving throw DC 14:
- Failed save: 6d10 fire damage and the creature gains embers (2 rounds duration).
- Successful save: half damage and no embers.
- Ember effect applied to any creature hit: at the start of their turn for the next 2 rounds they take 2d6 fire unless they use an action to extinguish (Athletics DC 12 to smother, or douse with water). While embered, disadvantage on Stealth and Perception (sight-based) checks for 1 round due to smoke/glare.
- Immediately after resolving the jets, roll initiative for the trap if desired; otherwise proceed to the next round with the trap acting at its initiative.
Round 1 (trap’s 1st turn after initiative)
- Smoke intensifies: center 30-foot corridor becomes heavily obscured; 10 feet beyond is lightly obscured. Ranged attacks have disadvantage while firing through heavy smoke; Perception checks reliant on sight have disadvantage.
- Trap action options (choose one or two):
- Sweep jets: trap adjusts internal valves to fire across a new set of three 20-foot lanes (you may overlap previous ones) — treat as repeated attacks identical to initial jets (Dex save DC 14, same damage).
- Maintain pressure: continue the jets on the same lanes, reinforcing embers (no stacking of embers beyond the 2-round limit; refresh duration for newly hit creatures).
- Ongoing embers: creatures who have embers take 2d6 fire at the start of their turns unless they extinguish them.
Round 2 (trap’s 2nd turn after initiative)
- Smoke further increases (heavier and longer-lasting). The trap can:
- Re-sweep jets to new lanes to force movement and split the party (target frontliners or ranged attackers).
- Optionally, the trap can aim jets to specifically target areas occupied by spellcasters/archers (use the same saving throw DC).
- New embers applied to anyone newly hit. Ember durations tick down from initial application.
Round 3 (if rune still active and mechanical not jammed)
- Floor collapse: heat-softened supports fail. The GM chooses (or rolls) a 10-foot square to collapse (preferably where players have sought cover or where they were forced to move).
- Creatures in the collapsing square make Dex save DC 14:
- Success: leap clear, take half the fall/trap damage (or land prone depending on how you narrate).
- Failure: fall 15 feet into pit or onto broken tiling — take 4d10 bludgeoning (or negotiate with spike damage if pit contains spikes) and may be knocked prone.
- Creatures in the collapsing square make Dex save DC 14:
- Rune eruption (if rune not suppressed): the medallion flares and releases a sustained arc of radiant-tinged flame that targets anyone attempting to pass through the medallion’s space or anyone near it:
- Wisdom save DC 14: success halves the 4d10 radiant+fire damage and avoids the stunned condition; failure takes full damage and is stunned until end of their next turn.
- After Round 3 the trap’s major escalation has occurred. If the rune is suppressed or mechanical jammed prior to Round 3, the escalation is prevented.
Dynamic hazards and targeting behavior
- Targeting decisions: the trap’s valve system lets it sweep jets to chosen lanes each round. Use this to:
- Target whoever is trying to disarm (pressure them).
- Force ranged attackers into the open by sweeping lanes where they take cover.
- Aim at party members who are separated from the group to split the party.
- Optional intelligent behavior (if you want it smarter): if the party includes a caster who’s the most dangerous to the trap (Dispel, Counterspell), have the trap aim jets to cut line-of-sight or to force the caster to move.
Suggested tactics and variations for different challenge levels
- Easier / lower-level (Setback / lower damage):
- Reduce initial jet damage to 2d10–4d10.
- Make the floor collapse a 5-foot partial sink rather than a full 15-foot fall.
- Lower save DCs by 2 (Dex/Wis DC 12).
- Default (Dangerous, level 7): use the stats above (6d10 initial, Dex save DC 14; embers 2d6; floor 4d10; rune eruption 4d10 radiant+fire Wis DC 14).
- Harder / Deadly:
- Raise initial damage to 10–12d10; raise save DCs to 16–18.
- Make rune eruption apply longer stunned condition or additional ongoing radiant burn (3 rounds).
- Expand the collapsing area to two adjacent 10-foot squares or have the collapse trigger hidden spikes with ongoing poison.
- Alternate themes/element swaps:
- Water/acid variant: replace fire with scalding steam/acid, swap fire damage with acid or bludgeoning + corrosive effects that damage metal armor.
- Clockwork variant: jets are replaced with spring-loaded blades (slashing + bleed).
- Tactical hints: if the party has a prepared caster with Dispel, the trap will often be neutralized quickly. To keep tension, force players to decide between disarming and rescuing an ally who’s embered or about to fall.
Interactions and improvisation (player creativity)
- Dousing embers: action to extinguish (Athletics DC 12 to smother, or use water). Dousing via water reduces ember damage and smoke effect for that creature.
- Pouring water into nozzles: if a PC gets to the access panel and pours a quantity of water into channels (requires an improvised check or DC 12), treat as halving initial jet damage for one subsequent firing; if rune is active, water less effective — reduces damage by half but doesn’t stop magical burst.
- Poles/long grapple: characters may attempt to depress or pry tiles from a distance; treat as Athletics/Acrobatics or an improvised tool check (DC 12–15 depending on approach) and risk of triggering.
- Opening hidden vent: Perception DC 13 to notice a cool draft/vent. Strength DC 12 to open jammed grate. Opening vent clears smoke for one round or more depending on how you rule.
Tracking the trap at the table — practical DM tips
- Use tokens or sticky notes: mark which creatures are embered and how many rounds remain; mark which 20-ft lanes are currently “hot”. Put a token on the collapsing 10-ft square when it’s primed.
- Use a simple chart on your DM screen for rounds: Round 0 (initial jets) → Round 1 → Round 2 → Round 3 (collapse/eruption). Cross off rounds as they pass.
- One-liner reminders: “Trap jets active — Dex save DC14; embers: 2 rounds; smoke heavy in center 30 ft.” Keep this near your initiative tracker.
- Narration matters: read the sensory cues (hiss, singed scent, faint glow) every round to remind players of the danger and what’s changing.
- Balance interactivity and pacing: let players make disarm attempts as actions during combat. If they succeed in jamming valves, stop further jet actions and cancel collapse if mechanical action disabled before round 3. If Dispel suppresses rune, negate rune eruption.
Examples of likely player choices and GM responses
- Party runs through corridor:
- PCs accept damage; jets fire immediately. Apply initial damage and embers. Trap may continue on initiative and target fleeing party with a follow-up sweep.
- One PC stays to jam:
- Allow Investigation DC15 to find panel, then Thieves’ Tools DC15 to jam (action + check). If successful before Round 3, floor collapse prevented. If fail by 5+, half jets fire immediately.
- Caster tries Dispel:
- Dispel Magic cast on the rune during combat: if the rune is an effect 3rd level or lower, Dispel stops it. If GM rules rune is stronger, require a spellcasting ability check (10 + rune level). A successful Dispel prevents rune eruption.
Round-by-round quick summary (for the DM)
- Trigger (Immediate): Initial jets fire — Dex save DC14; hit = 6d10 fire + embers (2 rounds).
- Trap rolls initiative.
- Trap turn (Round 1): Smoke increases (heavy in center 30 ft). Trap may sweep jets (same damage and saves). Embers deal 2d6 at start of affected creatures’ turns.
- Trap turn (Round 2): Smoke thickens; trap may resweep lanes; embers tick.
- Trap turn (Round 3): If rune still active:
- Floor collapse (choose 10-ft square): Dex save DC14 or fall 15 ft (4d10 bludgeoning); success half.
- Rune eruption: 4d10 radiant+fire; Wis save DC14 for half and avoid stun; failed save = stunned until end of next turn.
Optional quick reference (single glance)
- Initial save: Dex DC 14
- Ember damage: 2d6 at start of turn (2 rounds)
- Ember extinguish: action + Athletics DC12 or water
- Floor collapse: Dex DC14; fall 15 ft or 4d10 bludgeoning (half on successful save)
- Rune eruption: Wis DC14, 4d10 radiant+fire + possible stunned
Final DM-stagecraft notes
- Keep track of embers, lanes, and the countdown to round 3. Use markers and a short row of ticks (●● for embers; 3 ticks for rounds-to-collapse).
- Use sound and smell to build tension each time the trap acts: the hiss grows louder, mosaic sun-eye flares, bronze valves creak open — the players should feel the environment reacting.
- Be flexible with rulings if players try unusual solutions. The trap is designed to force decisions; reward creative tactics (e.g., using a carpet to smother nozzles, sacrificing a potion of water to douse a line).
- Adjust damage/DCs on the fly if the party is having a very different power level than expected: drop or add a die or lower/raise DC by 2 to keep it challenging but fair.
If you want, I can:
- Convert the round-by-round flow into a printable one-page handout for your DM screen.
- Re-tune the trap for a specific party level (e.g., APL 3 or APL 12) with revised damage/DCs and loot hooks.
- Change the elemental theme (water, acid, concussive steam, clockwork blades) and provide the alternate damage and environmental effects.
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