t1k:designer:systems:synergy-combos

Field	Value
Module	`systems`
Version	`1.7.2`
Effort	`high`
Tools	—

Keywords: balance, combos, game systems, synergy

How to invoke

/t1k:designer:systems:synergy-combos

Game Synergy & Combos

When This Skill Triggers

Designing item synergy systems (adjacency, set bonuses, class bonuses)
Balancing combo stacking and multiplicative effects
Preventing dominant meta builds (single strategy wins everything)
Designing synergy discovery UX (explicit hints vs hidden combos)
Tuning synergy depth (2-item weak vs 5-item gamebreaking)
Implementing build diversity enforcement
Scoring synergies for offering algorithms or AI recommendations

Orthogonality Principle

Every item must have at least 2 independent use cases:

Bad (one-trick):  Sword of Slaying — +50% damage to enemies with <20% HP
Good (orthogonal): Sword of Slaying — +30% damage; on kill: heal 5 HP

Rule: each item contributes to at least 2 synergy paths
Flat items (pure stat sticks, no synergy) are filler — max 20% of item pool

→ See references/synergy-design-patterns.md for orthogonality checklist, item archetype matrix

Synergy Types

Adjacency Synergies (grid-based inventory)

Trigger when 2+ items are placed next to each other in inventory grid
Strength tier: +10-20% stat boost (weak) — prevents mandatory placement
Maximum adjacency bonus: 35% per pair (beyond = feels mandatory, ruins freedom)
Formula: adjacency_bonus = base_bonus * min(adjacent_count, 4) * 0.7^(adjacent_count-1) (diminishing returns on 3rd, 4th adjacent prevents corner stacking)

Set Bonuses (collection-based)

2-item set: +15% to shared stat (discovery reward)
3-item set: +30% + unlock ability (noticeable power spike)
4-item set: +50% + transform ability (strategy-defining)
5+ item set: rarely worth forcing — too hard to assemble in roguelite

Never require full set for any ability — partial sets must feel rewarding

Type/Class Synergies (tag-based)

All items with tag X get +N% when player has M items of same tag
Bonus activates at 3+ same-tag items (prevents accidental activation)
Strength: +20-40% for 3 items, +50-70% for 5 items (significant enough to pursue)

→ See references/synergy-design-patterns.md for synergy type comparison, use-case matrix

Combo Scoring Formulas

Multiplicative Stacking (recommended)

total_multiplier = 1.0
for each active_synergy:
    total_multiplier *= (1 + synergy_bonus)

Example: 3 synergies at +30% each = 1.3 * 1.3 * 1.3 = 2.197x (not 1.9x additive)
Multiplicative feels exponential — use soft caps to prevent runaway power

Soft Cap Pattern

effective_bonus = raw_bonus / (1 + raw_bonus / cap_value)
# At cap_value=2.0: raw 2.0x becomes effective 1.33x; raw 5.0x becomes 1.67x

Apply soft cap at 3x total damage multiplier for combat balance
Separate caps per stat type: damage cap != heal cap != speed cap

→ See references/combo-scoring-formulas.md for stacking models, cap formulas, per-stat tuning

Build Diversity Enforcement

Dominant Strategy Prevention

Track win-rate per strategy archetype (top 3 items in winning runs)
If any archetype wins >40% of runs: nerf key item OR buff 3 alternatives
Design rule: at least 5 viable 3-item strategy cores before shipping

Diversity Metrics

Metric	Target	Red Flag
Strategy archetypes played	5+ in regular use	<3 viable strategies
Win rate spread across archetypes	<25% gap between best/worst	>40% gap
Synergy usage spread	No synergy used >60% of runs	One synergy >70%
Item acquisition diversity	Players pick 80%+ of item pool	20% of items never picked

→ See references/build-diversity-tuning.md for tuning workflow, A/B test criteria, meta reset strategies

Synergy Discovery UX

Explicit vs Hidden Spectrum

Style	Examples	When to Use
Fully explicit	Tooltip shows all synergy tags, % bonus shown in real-time	Tutorial / beginner mode
Hint-based	Item border glows when synergy active; no numbers	Core mobile experience
Discovery-based	No hints; players must experiment	Hardcore PC roguelikes

Recommended (BackpackCrawler): Hint-based — border glow on adjacency, “SET 2/3” counter visible
Reveal synergy name and value on hover/tap AFTER it activates (not before)
Show synergy “preview” (greyed-out) when 1 item away from set completion

Anti-Patterns

#	Anti-Pattern	Problem	Fix
1	One-trick items	No strategy flexibility	Add second synergy path
2	Mandatory adjacency placement	Reduces grid freedom	Cap adjacency bonus at 35%
3	Full-set required for ability	Punishes partial strategies	Partial sets must reward too
4	Additive stacking only	Diminishing feel at high counts	Mix multiplicative + soft cap
5	Single dominant combo	Players always chase same path	Nerf + buff 3 alternatives
6	Hidden synergies with no hints	Discovery becomes frustration	Border glow at minimum

Cross-References

puzzle-game-design — adjacency bonus implementation in polyomino grid
rpg-game-design — item power budgets that synergy bonuses must stay within
game-shop-offering — synergy scoring used by offering algorithm
game-balance-tools — TTK validation with synergy multipliers applied
game-roguelike-design — synergy power curves must align with run difficulty arc

Reference Files

File	Coverage
`references/synergy-design-patterns.md`	Synergy types, orthogonality checklist, archetype matrix
`references/combo-scoring-formulas.md`	Stacking models, soft caps, per-stat tuning
`references/build-diversity-tuning.md`	Diversity metrics, anti-dominance workflow, meta resets

Gotchas

Orthogonality > stack-everything — a system where every pair synergizes feels like one big stat; players need to discover the combos that DON’T work.
Dominant meta is inevitable; embrace + balance is faster than nerf-pin — buff the underused before nerfing the dominant.
Adjacency synergies on mobile screens must be telegraphed — a 3x3 grid synergy that requires squinting kills the loop.