The Deepening
Updated: 2026-02-26
The underhive is not a static place. It breathes, shifts, and rots. As the campaign progresses, the zones of Sump Sink-17 deteriorate - toxic floods rise, ancient machinery groans to life, and the things that live in the dark grow bolder. This is The Deepening.
Overview
The Deepening is a cyclical escalation system that tracks how dangerous each zone becomes over the course of the campaign. Contamination rises, peaks, and then recedes - a tidal rhythm that gives the campaign an indefinite lifespan. Each zone has a single Contamination Level (0-5) that the Arbitrator tracks. This one number drives four interlocking mechanics:
- Contamination Effects - always-on battlefield conditions that stack as contamination rises
- The Sump Rises - zone reclassification when contamination hits critical thresholds
- Hazard Rolls - per-battle random hazards scaled to contamination
- Battle Scars - post-battle territory degradation
The Arbitrator tracks three numbers - one per zone. That’s it.
The Tidal Cycle
The Deepening is not a one-way slide into oblivion. The underhive breathes - contamination rises over successive arcs, peaks, and then recedes as ancient mechanisms reassert themselves and the horrors of the deep withdraw. This cycle repeats indefinitely, giving the campaign a rhythm of escalation and relief.
Each full cycle has two phases:
- The Deepening - Contamination rises at arc boundaries, following the schedule below. The underhive gets worse. This phase lasts approximately five arcs.
- The Receding - Triggered by a climax scenario at peak contamination (see Sealing the Seep). Contamination drops at the same rate it rose, one level per zone per arc boundary, following the same stagger (the Sump leads, the Sprawl trails). Zone reclassifications fully revert when contamination drops below their thresholds. This phase also lasts approximately five arcs.
When contamination returns to its starting values (Sump 1, District 0, Sprawl 0), the next arc boundary begins a new Deepening. The gangs get a brief respite - then the cycle starts again. Each full cycle spans roughly ten arcs (50 Cycles).
The Arbitrator should announce which phase the campaign is in at each arc boundary. The phase does not change any of the four core mechanics - they always use the current contamination level, whether it is rising or falling.
Contamination Schedule
Contamination rises at arc boundaries, tied to the Narrative Arcs. The underhive gets worse whether the gangs are ready or not.
The Deepening (Rising Phase)
| Event | Sump | Drowned District | Sprawl |
|---|---|---|---|
| Campaign Start | 1 | 0 | 0 |
| End of Arc I (Cycle 5) | 2 | 1 | 0 |
| End of Arc II (Cycle 10) | 3 | 2 | 1 |
| End of Arc III (Cycle 15) | 4 | 3 | 2 |
| End of Arc IV (Cycle 20) | 5 | 4 | 3 |
| End of Arc V (Cycle 25) | 5 | 5 | 4 |
The Sump hits maximum contamination (5) at the end of Arc IV. The Drowned District catches up in Arcs V, but the Sprawl never exceeds contamination level 4. The peak is reached at the end of Arc V and this is when the Sealing the Seep climax scenario is triggered.
The Receding (Falling Phase)
Once the climax scenario concludes, contamination begins to fall. The recession mirrors the rise - one level per zone per arc boundary, with the Sump leading and the Sprawl trailing.
| Event | Sump | Drowned District | Sprawl |
|---|---|---|---|
| After Sealing the Seep | 4 | 4 | 4 |
| Next arc boundary | 3 | 3 | 3 |
| Next arc boundary | 2 | 2 | 2 |
| Next arc boundary | 1 | 1 | 1 |
| Next arc boundary | 1 | 0 | 0 |
The Sump never drops below Contamination 1 - it is always dangerous. The Drowned District and the Sprawl return to Contamination 0. Once all zones reach their starting values, the next arc boundary begins a new Deepening.
Mechanic 1: Contamination Effects
Effects are always-on and cumulative - a zone at Contamination 3 has all effects from levels 1, 2, and 3 active simultaneously. No rolling needed to determine what’s active; just check the zone’s current level.
| Level | Effect | Flavour |
|---|---|---|
| 0 | None | As safe as the underhive gets. |
| 1 | Bad Air - Each End Phase, fighters not in cover roll D6; on a 1, suffer a Flesh Wound. | The air tastes wrong. |
| 2 | Unstable Ground - Fighters who run or charge must pass an Initiative check or become Pinned. | The floor groans. Dark pools collect in the low points. |
| 3 | The Fog Rolls In - From Round 3+, visibility is reduced to 12” (beyond 12” counts as full cover). | Thick acrid mist seeps from below. |
| 4 | Things in the Dark - At the start of each round, the non-Priority player places a Beast marker within 6” of a board edge (not within 8” of any fighter). Any fighter ending their activation within 3” of a Beast marker takes a S3 AP- D1 hit; then remove the marker. | Skittering. Shapes at the edge of the lumen-light. |
| 5 | The Sump Hungers - All above effects apply. Additionally, fighters taken Out of Action count as Captured (rescued only on a 5+ in a Rescue scenario). | The dark has teeth. |
Mechanic 2: The Sump Rises
When a zone hits Contamination 3, it takes on characteristics of the zone below it. The rising sump doesn’t just make things harder - it reshapes the map.
Drowned District at Contamination 3 (End of Arc III)
- Gains Pitch Black rules (all territories in the zone)
- Income modifier rises from +50% to x2 (matching the Sump)
- Territory cap increases from 3 to 4 per gang
Sprawl at Contamination 3 (Arc IV+)
- Gains +50% income modifier (matching the Drowned District)
- The Arbitrator designates D3 Sprawl territories as “Flooded” - these count against the gang’s Drowned District territory cap instead of having no cap
The Receding: Zone Reversal
Zone reclassifications are fully reversible. When contamination drops below the threshold that triggered a reclassification, the changes revert:
- Drowned District drops below Contamination 3: Pitch Black rules are removed. Income returns to +50%. Territory cap returns to 3 per gang.
- Sprawl drops below Contamination 3: The +50% income modifier is removed (income returns to base). Flooded territories are redesignated as normal Sprawl territories and no longer count against the Drowned District cap.
Narratively, the waters recede, the fog lifts, and the creatures retreat into the deeper darkness. The zones are scarred but functional - hab-blocks dry out, lumen-strips flicker back to life, and the gangs reclaim what was lost.
Mechanic 3: Hazard Roll
Before deployment in any battle, roll D6. If the result is equal to or less than the territory’s current contamination level, roll on the Deepening Hazard Table below. This hazard applies on top of the always-on contamination effects.
At Contamination 0, no hazard roll is needed - a D6 can never roll 0 or less.
Deepening Hazard Table (D6)
| D6 | Hazard | Effect |
|---|---|---|
| 1 | Toxic Downpour | Each End Phase, fighters not fully within or under terrain take a S2 hit. |
| 2 | Sludge Jellies | Place D3+1 Sludge Jelly markers on the battlefield. Fighters within 1” must pass a Strength check or become Engaged with the jelly (S3 T3 W1). |
| 3 | Spore Cloud | Each round, a 3” blast drifts from the centre of the board (Scatter + D6”). Fighters under it must pass a Toughness check or count as failing a Nerve test. |
| 4 | Critter Swarm | The first fighter taken Out of Action on each side spawns a 3” hazard zone centred on their position. Fighters entering or starting an activation in the zone take a S2 hit. |
| 5 | Structural Collapse | At the start of Round 3, the Priority player selects one terrain piece and collapses it. Fighters on or within 1” take a S5 AP-1 D2 hit. The terrain becomes dangerous ground for the rest of the battle. |
| 6 | The Deep Tremor | At the start of Round 2, all fighters must pass an Initiative check or become Pinned. One random corridor or doorway (determined by the Arbitrator) becomes impassable for the rest of the battle. |
Mechanic 4: Battle Scars
After every battle, the winner rolls D6 on the table below. In a draw, both players roll.
| D6 | Result | Effect |
|---|---|---|
| 1–2 | No Lasting Damage | The territory weathers the fighting. No effect. |
| 3 | Structural Damage | Territory income is permanently reduced by 10 credits (minimum 0). |
| 4 | Toxic Spill | The territory’s contamination increases by +1 (capped at its zone’s current contamination level +2). |
| 5 | Creature Nest | The next battle fought at this territory automatically triggers a Hazard Roll result (no roll needed - the hazard always activates). Then the nest is cleared. |
| 6 | Salvage Find | The territory’s holder gains D6x10 credits at their next income collection. Then the find is removed. |
Reward Scaling
The Deepening isn’t just punishment - the underhive rewards those who brave its worst.
- Contamination Bonus: Winning a battle at Contamination 3 or higher grants +1 XP to any single fighter of the winner’s choice.
- The Sump Rises income boosts (see Mechanic 2) compensate for the increased danger of operating in deteriorating zones.
Per-Battle Quick Reference
Before deployment:
- Check the territory’s Contamination Level
- Note which Contamination Effects are active (all levels up to and including the current level)
- Roll for Hazard (D6 ≤ Contamination Level = roll on Hazard Table)
During the battle:
- Apply all active effects and any triggered hazard
After the battle:
- Winner rolls on the Battle Scars table (both players roll on a draw)
The Receding
The pressure eases. The black water sinks back into the cracks. Lumen-strips flicker to life in corridors that have been dark for cycles. The things in the deep grow quiet - not gone, just waiting. The gangs emerge from their bolt-holes, blinking, and begin the work of reclamation. But the underhive remembers. It always remembers.
During The Receding, no new mechanics are introduced. The existing four mechanics - Contamination Effects, The Sump Rises, Hazard Rolls, and Battle Scars - continue to function exactly as written, using the current (falling) contamination level. As contamination drops, effects peel away from the top: the first thing to go is The Sump Hungers (level 5), then Things in the Dark (level 4), and so on.
The Receding is not safety. It is a reprieve. Contamination still applies, hazard rolls still trigger, and battle scars still accumulate. The underhive is simply less hostile than it was at the peak - and every gang knows the tide will turn again.
Sealing the Seep
The Seep is open. Black water rises from the lowest point of Sump Sink-17, and with it come things that should have stayed buried. The only way to stem the tide is to reach the ancient machinery beneath the Seep and force it to life. Every gang in the Sink knows what’s at stake. Not all of them agree on what should be done with the machinery once it’s activated.
This is the repeating climax scenario that triggers The Receding. It is played when all three zones reach Contamination 5 (or when the Arbitrator determines peak contamination has been reached).
Setup
- Location: The Seep, the lowest accessible point of the Sump (Zone 3)
- Players: All active gangs may participate. Each gang deploys their full available roster (up to the scenario’s fighter limit, determined by the Arbitrator based on player count - 10 per gang is recommended)
- Battlefield: A large board (ideally 4’x4’ or larger) representing the cavern of the Seep. The centre of the board contains the Seep Machinery - an ancient device partially submerged in black water. Three Activation Points are placed equidistant around the machinery, each 12” from the centre
Special Rules
- Pitch Black: The entire battlefield uses Pitch Black rules
- Contamination 5: All Contamination Effects (levels 1-5) are active throughout the battle. This is the worst the underhive has to offer
- The Seep: The central 6” of the board is shallow black water. Fighters moving through it halve their Movement characteristic. Fighters ending their activation in the water must pass a Toughness check or suffer a Flesh Wound
- Things From Below: At the start of each round after the first, place D3 Beast markers (as per the Things in the Dark contamination effect) within 6” of the Seep. These are in addition to any markers placed by the Contamination 5 effect
Objectives
Each Activation Point must be held by a fighter (within 1”, no enemy fighters within 1”) at the end of a round to become active. An Activation Point can be deactivated by an enemy fighter reaching it and spending a basic action.
When all three Activation Points are simultaneously active at the end of any round, the machinery activates and The Receding begins. The battle ends immediately.
Victory
The gang that holds the most Activation Points when the machinery activates is the Victor. In a tie, the gang with the most fighters still standing wins. The Victor gains:
- The Seep-Wright: One fighter of the Victor’s choice gains the Seep-Wright title. This fighter gains +1 Toughness permanently (representing exposure to and survival of the Seep’s influence). The title is lost if the fighter dies
- Shaper of the Recession: The Victor’s player chooses one zone. That zone’s contamination drops by an additional 1 at the first arc boundary of The Receding (giving it a head start on recovery)
- D6x10 credits from salvage recovered during the activation
If the Battle Stalls
If no gang can activate all three points by the end of Round 8, the machinery activates on its own - the ancient systems have their own agenda. The Receding begins with no Victor. No gang receives the rewards above.
Replaying the Scenario
Each time the campaign reaches peak contamination, the Sealing the Seep scenario is played again. The Arbitrator is encouraged to vary the battlefield layout and Activation Point placement between cycles to keep the scenario fresh. The narrative framing shifts with each repetition - perhaps the machinery degrades, or something new has nested in the Seep since the last time.