Deck Expansion Impact — headline statistics
Each Spirit Island expansion adds cards to the Minor, Major, Fear, Event, and Blight decks. Those additions dilute the base pool — drawing a card from the Fear deck at Base-only is a different probability distribution than drawing one from Base+B&C+JE+NI. This chapter renders the per-expansion-combo impact across all five decks, using deck data deterministically fetched from spiritislandwiki.com via scripts/wiki-fetch.py and analyzed by scripts/deck-stats.py + scripts/deck-simulate.py.
Pool sizes per expansion combo
| Combo | Minor | Major | Fear | Event | Blight |
|---|---|---|---|---|---|
| Base only (Horizons + Base game) | 36 | 22 | 15 | 0 | 2 |
| Base + B&C | 66 | 43 | 30 | 23 | 8 |
| Base + JE | 69 | 46 | 21 | 30 | 9 |
| Base + B&C + JE | 99 | 66 | 36 | 53 | 15 |
| All expansions (Base + B&C + JE + NI + Promos) | 100 | 78 | 50 | 62 | 23 |
| NI additions only (delta from JE) | 1 | 13 | 9 | 9 | 8 |
Pool sizes count only cards that are still in use. Nature Incarnate’s “Dropped Cards” list (NI rulebook p.5) removes Outpaced, War Touches the Island’s Shores and A Strange Madness Among the Beasts (Events), Growth Through Sacrifice (Minor) and Tipping Point (Blight); Far-off Wars Touch the Island and Roiling Bog and Snagging Thorn replace two of them. Jagged Earth replaced the Branch & Claw Major Sea Monsters with an updated card. The Event counts include Slave Rebellion, which is added only against France, so without France each pool that includes Branch & Claw is one Event smaller (all expansions: 61 + Slave Rebellion). These totals match the Steam game’s allowed pools (Minors 100, Majors 78, Fear 50, Events 61 + Slave Rebellion, Blight 23; data/references/rules/open-questions.md, Q15).
Expected per-game outcomes (Monte Carlo, 5 000 trials × 8 rounds × 1 player)
Each trial plays 8 turns with no Adversary or Scenario (scripts/deck-simulate.py, seed 42). The rules it follows:
- Fear. The Fear Pool holds 4 Fear per player, so solo each Fear Card costs 4 Fear; leftover Fear carries over. The Fear Deck is 9 cards split 3/3/3 by the Terror Level dividers. Earning the 3rd card reveals the Terror Level II divider and earning the 6th reveals Terror Level III, at once; earning the 9th is a Fear victory. Earned cards resolve in the next Fear step at the Terror Level current then (core rulebook setup and “Fear”;
open-questions.mdQ6, Q7). - Events. One per turn. The Turn-1 Event is drawn and discarded without resolving (Jagged Earth rulebook p.12), so 8 turns draw 8 Events and resolve 7. Slave Rebellion is left out (no France).
- Blight. One Blight Card at setup with 2 per player + 1 Blight. A second card is drawn only when a Still-Healthy card’s pool runs out (Jagged Earth rulebook).
Two inputs are unsourced placeholders, not measured rates: Fear generated per turn (Gaussian, mean 2.5, σ = 1) and net Blight per turn from Turn 2 (Gaussian, mean 0.5, σ = 1). Treat every figure that depends on them as illustrative. “Spirit favor” and “Invader favor” are keyword-phrase hits on resolved Fear and Event texts (see Event Deck Risk Profiles). Values are means; the 95% confidence intervals are in the JSON output.
| Combo | Fear cards earned | Resolved at TL I / II / III | “N Fear” text | Events drawn / resolved | Blight cards | Spirit favor | Invader favor | Net favor |
|---|---|---|---|---|---|---|---|---|
| Base only (Horizons + Base game) | 4.64 | 1.99 / 2.51 / 0.13 | 0.00 | 0 / 0 | 1.00 | 1.50 | 0.00 | +1.50 |
| Base + B&C | 4.62 | 1.99 / 2.51 / 0.12 | 3.19 | 8 / 7 | 1.00 | 6.69 | 5.44 | +1.25 |
| Base + JE | 4.64 | 1.99 / 2.52 / 0.13 | 3.50 | 8 / 7 | 1.09 | 10.18 | 5.11 | +5.07 |
| Base + B&C + JE | 4.61 | 1.99 / 2.50 / 0.12 | 3.40 | 8 / 7 | 1.05 | 8.59 | 5.27 | +3.33 |
| All expansions (Base + B&C + JE + NI + Promos) | 4.63 | 1.99 / 2.51 / 0.13 | 4.29 | 8 / 7 | 1.08 | 8.79 | 4.96 | +3.83 |
| NI additions only (delta from JE) | 4.62 | 1.99 / 2.51 / 0.13 | 9.08 | 8 / 7 | 1.14 | 9.89 | 3.10 | +6.79 |
Key readings
- Base-only has no Event deck. A Blight Card, if used, comes from the 2 base cards (the core game also allows the Invader Board’s printed Blight space instead), and the Invader, Fear and Power decks are still hidden, shuffled orders.
- +B&C adds the Event deck (23 cards, 22 without France) and 6 Blight Cards (8 with the base 2), and makes a Blight Card required (Branch & Claw rulebook). An 8-turn game draws 8 Events and resolves 7.
- The keyword counts come out net positive in every combo (+1.25 with B&C, +5.07 with JE, +6.79 for NI’s cards alone). They sum resolved Fear and Event texts; for scale, the base-only row, which has Fear Cards only, nets +1.50. Read the Event share as a limit of the phrase classifier rather than a finding: the designer intended Events to be slightly negative on average (darker, BGG 2506650). See Event Deck Risk Profiles.
- Fear cards earned depend only on the Fear rate, not the expansion. At the placeholder rate, 8 turns generate about 8 × 2.5 = 20 Fear; leftover Fear short of a full card averages about 1.5, so (20 − 1.5) ÷ 4 ≈ 4.6 cards, as simulated. Cards 1–2 resolve at Terror Level I and cards 3–5 at II; Terror Level III needs 6 cards (24 Fear solo), reached in about 1 trial in 9. Each card costs 4 Fear per player, so at the same total rate a 2-player game earns half as many (2.07 cards in a 2 000-trial run with
--players 2). - Blight cards drawn is 1 plus the Still-Healthy draws. Base and B&C have no Still-Healthy cards, so exactly 1.
Cross-references
- Fear Deck Expected Value — per-expansion Fear-card breakdown + Terror Level distribution.
- Event Deck Risk Profiles — balanced vs. skewed events by expansion.
- Blight Deck Severity — how catastrophic each expansion’s Blight additions are.
- Token Dilution — per-token-type frequency across pools.
- Minor vs. Major Draft Rates — how Minor/Major draft composition shifts.