1. The Campfire Dilemma: Immediate Survival vs Long-Term Tempo
In Slay the Spire 2, resting recovers a fixed 30% of your Maximum HP (rounded down), unless modified by specific relics such as the Eternal Feather or Regal Pillow. On paper, 30% health represents substantial resilience. However, an unupgraded deck incurs higher damage in every subsequent fight because combats take 1 to 2 extra turns to resolve.
The fundamental rule of high-Ascension climbing is that upgrades save HP over time, while rests only replenish spent HP. If upgrading a foundational card (like Bash+, Carnage+, or Uppercut+) reduces the length of an upcoming combat from 4 turns to 3 turns, it prevents an entire cycle of incoming enemy attacks—often mitigating 15 to 22 incoming damage in a single encounter.
2. Mathematical Formulation of the Decision Matrix
Our optimizer evaluates two opposing variables before issuing a recommendation:
Variable A: Immediate Lethal Risk R(lethal)
R(lethal) = f(HP_current, D_expected, Var_draw)
Where D_expected is the baseline turn 1–3 burst potential of the subsequent room (25–45 for Act 1 Elites such as Gremlin Nob or the new STS2 Sentinels), and Var_draw represents the variance of drawing defensive answers without card draw relics.
Variable B: Cumulative Upgrade Amortisation V(upgrade)
V(upgrade) = Sum of HP_saved across all remaining fights before the Act Boss
If your candidate upgrade reduces damage taken by an average of 6 HP per encounter and you have 5 floors remaining before the Act Boss, the gross expected value of Smithing is +30 HP, cleanly outstripping a +22 HP rest heal.
3. Three Critical Threshold Rules Every Climber Must Know
Rule 1: The Elite Burst Ceiling (The 40% Floor)
If entering an Act 1 Elite with less than 40% Max HP and no high-impact defensive potions (like Ghost in a Jar or Fairy in a Bottle), resting is mandatory. Slay the Spire 2 elites penalise slow setups with devastating turn-2 debuffs and heavy vulnerable hits.
Rule 2: The Boss Amortisation Window
When a campfire is immediately preceding the Act Boss (1 floor away), the math flips: the upgrade only affects a single fight. Smithing here is only justified if the specific upgrade provides Boss-scaling (e.g. Demon Form, Noxious Fumes, or End of Days) that fundamentally dictates whether the boss is defeatable.
Rule 3: Potion Buffer Valuation
A single Block Potion or Weak Potion can effectively absorb 12–20 damage in a pinch. If your HP sits in the "Greedy" amber band (45–60%) but your potion belt is fully stocked, you should lean toward Smithing to preserve momentum.
4. Worked Example: Act 1 Lagavulin Scenario
The Situation: The player holds an unupgraded Uppercut (13 damage, 1 Weak, 1 Vulnerable). The next floor is guaranteed to be an Elite. Resting would bring the player from 32 HP to 53 HP (+21 HP).
The Math Comparison:
- Rest Path: Player enters the fight with 53 HP. Uppercut applies 1 Weak and 1 Vulnerable. The elite survives for 4 attack cycles, dealing ~42 gross damage. Player leaves the combat with ~11 HP remaining and an unupgraded deck.
- Smith Path: Uppercut+ deals 13 damage and applies 2 Weak and 2 Vulnerable. The additional turn of Vulnerable allows the player's following attacks to deal 50% extra damage, ending the fight a full turn earlier. The elite only attacks 3 times, dealing ~26 gross damage. The player exits the fight with 6 HP, but possesses a permanently upgraded core card that accelerates every future floor.
Optimizer Conclusion: While resting appears safer on paper, having Uppercut+ permanently transforms combat pacing. If the player possesses even a basic Strength or Fire potion, Smithing is mathematically optimal.
5. Frequently Asked Questions Regarding Campfire Math
Does high Ascension change campfire heal percentages?
At Ascension 5 and above, healing at rest sites is frequently capped or adjusted in scaling encounters. More critically, higher enemy damage on higher Ascensions raises the expected damage baseline, tightening the lethal threshold and making bad smith decisions instantly fatal.
Should I ever Lift (Girya) or Dig (Shovel) instead of Smithing?
Digging for a relic provides variable EV depending on relic rarity pools. As a heuristic, an immediate card upgrade to your primary damage source carries higher deterministic value than a random Common or Shop relic in Act 1. Shovel gains massive relative value in late Act 2 once your primary deck shell is already upgraded.