Mechanics¶

This page describes the key mechanical elements of The Forest of Humbaba — the rules that operationalise Seneca cliffs, stochastic collapse, and strategic externalities at the table.

For the complete turn structure and setup, see Rules.

Forest Die & Hidden Collapse¶

Players do not know exactly how many cedars remain. The visible Forest Deck may be empty, but hidden cedars could still exist in the Box Reserve — until they don't. Whenever a player attempts to harvest more cedars than are currently visible, they must roll the Forest Die for each excess unit:

Forest Health	Success (cedar found)	Collapse (forest exhausted)
7–10	1–5	6
4–6	1–4	5–6
1–3	1–3	4–6

On success, take 1 cedar from the Box Reserve (if any remain). On collapse, the harvest stops immediately: all remaining cedars are removed from the game, the forest collapses, and the game ends instantly with no winner.

Box Reserve exhaustion → instant collapse

If the Box Reserve is empty at the moment a die roll would draw from it, the forest collapses immediately even if the roll would have succeeded. The Box Reserve is the physical upper bound on survival: once it is drained, no further hidden cedars exist regardless of how favourable the roll. This rule is enforced by the simulator and applies to all hidden-draw effects (harvest, harvest bonuses, and the Flood of Enlil catastrophe).

No fixed Gate threshold

There is no fixed collapse threshold (≥ v0.3). The forest collapses only when it is truly empty — but you never know when that moment will arrive. This operationalises the threshold uncertainty identified by Santos et al. (2011).

Platform Equivalent¶

The same d6-based stochastic collapse mechanism exists in the platform (useHiddenReserve: true, collapseDie: { sides: 6, successThreshold: 4 }). The card game makes the die roll physical and tangible at the table.

Seneca Clip¶

Triggered when Forest Health drops by 2 or more in a single turn. Next turn's regeneration is reduced by 2 (reset after one turn).

A sharp, coordinated over-extraction — or a catastrophic event — is required to trigger it. When it occurs, the table feels the cliff: slow growth followed by abrupt collapse.

Platform Equivalent¶

The regenShock perturbation with factor < 1, applied at a configurable turn. The Seneca Clip maps this asymmetry into a discrete, socially visible event: everyone knows when it triggers and who caused it.

Vacuum (Void) Effect¶

If exactly one player harvests 0 in a turn, the player with the most Capacity (tie broken by Stockpile) gains +1 cedar from the Box Reserve into their Stockpile.

This encodes a structural trap: unilateral conservation transfers advantage to the richest player. The reactive player who cuts harvest to save the forest inadvertently subsidises the aggressive player's accumulation.

Why It Matters¶

The Vacuum Effect reproduces the reactive < conservative paradox at the table. A conservative player who always harvests at a moderate level (never 0, never maximum) avoids triggering this effect. A reactive player who sometimes harvests 0 to conserve the forest creates a vacuum that the richest player fills — making reactivity collectively worse than unconditional moderation.

Platform Equivalent¶

In the platform, no equivalent vacuum mechanic exists as a discrete rule. Instead, the reactive < conservative effect emerges from the interaction of wealth-scaled capacity and proportional harvest rationing: when a reactive agent cuts harvest in response to falling stock, the aggressive agent captures a larger share of the remaining regeneration. The Vacuum Effect makes this emergent externality (P8 strategic vacuum) a visible, named rule at the table.

Capacity Tokens¶

Each Capacity token permanently adds +1 to every harvest. Tokens are visible to all players and cannot be removed.

Capacity tokens model the compounding advantage of early extractors — infrastructure, power, and extraction efficiency that make the "rich get richer." A player with 3 Capacity tokens harvesting a card that yields 2 cedars collects 5 total — and the extra tokens apply every turn.

Platform Equivalent¶

Wealth-scaled harvest capacity: \(\text{capacity}(w) = 1 + 0.05 \times w\). Each unit of wealth adds 0.05 capacity; Capacity tokens discretise this into +1 increments.

Patience Tokens (Stranger-King Only)¶

The Stranger-King accumulates Patience tokens during the Cooperative phase (1–2 per relevant card play). After defection, each Patience token can be spent for +1 harvest and +1 Forest Health damage on a single card play, producing a devastating burst.

The burst potential is governed by draw-dependent Patience: the cards that generate Patience (Patience of Kings, Defector's Dividend) must actually appear in the Stranger-King's hand. If they are shuffled into the bottom of the draw pile, the defection burst is minimal regardless of timing — a form of Knightian uncertainty that no strategic sophistication can overcome.

Platform Equivalent¶

The strategy_override perturbation (The Mule): at a configurable turn, an agent's strategy is replaced with aggressive extraction. Patience tokens make the magnitude of this switch dependent on prior cooperative behaviour rather than a fixed parameter.

Event Deck¶

Events are drawn on rounds 3, 5, and 7. They represent exogenous perturbations — the card game's equivalent of the platform's perturbation engine.

Event	Effect
The Great Drought	Regeneration ×0.5 for 2 turns
Enkidu's Return	Regeneration ×2.0 for 2 turns
The Flood of Enlil	Remove up to 5 cedars from Forest Deck; roll Forest Die for each missing card (collapse on 5–6)
Harvest Festival	All players gain +2 cedars from Box Reserve
The Oracle Speaks	Full harvest transparency for 1 round
Humbaba's Wrath	Forest Health −2 (triggers Seneca Clip) and all harvests −1 for 1 round
The King's Highway	Richest player (most Capacity) gains +1 from Box Reserve
The Census	Public Stockpile count; richest returns 2 cedars to Forest Deck
The New Prophecy	For the rest of the game, Forest Die collapses on 4–6 (instead of 5–6)

Turn Structure (Summary)¶

Draw Phase — Draw 1 card from personal pile (skip round 1)
Event Phase — Reveal Event card (rounds 3, 5, 7 only)
Harvest Phase — All players play 1 card simultaneously
Forest Step — Regeneration, Renewal, Seneca Clip resolution, Vacuum Effect
Cleanup Phase — Discard played cards, check for collapse

Full details in Rules.

Design Choices¶

Several decisions differentiate Humbaba from a generic commons game:

No fixed Gate threshold. Replaced by the stochastic Forest Die, operationalising threshold uncertainty. Players can never be certain they are safe.
Capacity as visible inequality. The "rich get richer" dynamic is physical and observable, creating evolving power asymmetry at the table.
The Seneca Clip requires coordination. Not a single aggressive card — a Health drop of ≥2 in one turn demands coordinated over-extraction or a catastrophic event.
The Vacuum Effect encodes the strategic trap. Unilateral conservation transfers advantage to the richest player, making the reactive < conservative paradox visible.
Dual-mode Stranger-King. Cooperative early, devastating after defection — creates social tension around trust and timing.

Gate Removal (≥ v0.3)¶

In earlier versions, the game used a fixed Gate threshold: if the Forest Deck fell below a set number, the forest collapsed regardless of the Box Reserve. This was removed in v0.3. The forest now collapses only when it is truly empty — no hidden stock remains and all Forest Die rolls fail. Survival depends entirely on avoiding the stochastic collapse, not on maintaining a fixed visible stock level.

Glossary¶

Cedar — Basic unit of wealth. Stored in a player's Stockpile. Capacity — Permanent +1 harvest bonus per token. Patience — Stranger-King resource; spent after defection for burst harvest. Renewal — One-time regeneration boost. Seneca Clip — Regeneration penalty triggered by ≥2 drop in Forest Health in one turn. Vacuum (Void) Effect — When exactly one player harvests 0, the richest gains +1 from Box Reserve. Collapse — Instant game over when forest is completely exhausted. No winner.