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 |
Expected per-game outcomes (Monte Carlo, 5 000 trials × 8 rounds × 1 player)
Each trial simulates 8 invader rounds using a Gaussian fear-generation model (mean 2.5 fear/turn, σ=1) and sequential draws from the Fear/Event/Blight decks per expansion combo. Fear threshold transitions at TL1→TL2 (4 fear) and TL2→TL3 (8 fear) trigger Fear-card draws. Events draw once per turn (when an Event deck is in play). Blight cards draw at game start + on track-fill. Values are means; the 95% confidence intervals are reported in the JSON data, but omitted here for readability.
| Combo | Fear drawn | Fear output | Events | Blight cards | Spirit favor | Invader favor | Net favor |
|---|---|---|---|---|---|---|---|
| Base only (Horizons + Base game) | 2.00 | 0.00 | 0.0 | 0.00 | 0.65 | 0.00 | +0.65 |
| Base + B&C | 2.00 | 3.49 | 8.0 | 1.89 | 7.03 | 5.94 | +1.09 |
| Base + JE | 2.00 | 3.97 | 8.0 | 1.89 | 10.72 | 5.86 | +4.87 |
| Base + B&C + JE | 2.00 | 3.79 | 8.0 | 1.89 | 9.05 | 5.88 | +3.17 |
| All expansions (Base + B&C + JE + NI + Promos) | 2.00 | 4.66 | 8.0 | 1.90 | 9.20 | 5.55 | +3.65 |
| NI additions only (delta from JE) | 2.00 | 10.00 | 8.0 | 1.90 | 10.32 | 3.56 | +6.76 |
Key readings
- Base-only is un-eventful by design. No Event deck, 2 Blight cards only. Games are deterministic up to the spirits’ own plays.
- +B&C adds the Event deck (23 cards) and the full Blight deck (8 cards). That’s ~+8 events drawn per game — significant stochastic variance injection.
- +JE events skew slightly more spirit-favorable (net +4.87 hits/game vs. +1.09 for B&C alone). JE Minor/Major pools also dilute the base element distribution — see per-deck chapters.
- NI events are the most spirit-favoring when counted alone (+6.76), but NI adds only 9 events (small pool, high variance per game).
- Fear drawn stabilizes at ~2 cards/game across combos (2 threshold crossings × 1 draw each at 1-player scale). At higher player counts the thresholds scale linearly — expected fear drawn drops per player.
Cross-references
- Fear Deck Expected Value — per-expansion Fear-card breakdown + stage 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.