Build Diversity — many viable strategies

What it is. The discipline of keeping many builds viable — so a player assembling weapons, cards, relics, or skills faces choices, not a solved optimum. The enemy of build diversity is the dominant strategy: the one loadout that outperforms all others, collapsing the build screen into a lookup.

Player fantasy / why it’s fun. Expression. “This is my run — poison stacks, or crit-and-glass, or turtle-and-scale.” Build diversity is what makes a roguelite replayable: the mechanics are fixed, but the strategy you author is new each time.

When to use / when NOT

Use it when…	Less critical when…
The player composes from many parts	There’s one fixed kit
Replayability comes from strategy variety	Content variety carries replay instead
Synergies/`system-status-effects` exist	The game is short/linear

Variants — where the diversity lives

Source	Diversity from	Anchor
Loadout	pick a weapon/kit, whole run reorganizes	`anchor-hades` weapons/aspects
Synergy engine	parts combo multiplicatively	`anchor-slay-the-spire` archetypes; `anchor-balatro` jokers
Passive stacking	choices compound into a style	`anchor-vampire-survivors` evolutions
Skill tree	branch exclusivity forces identity	`system-skill-trees`
Draft	reward-of-N shapes the deck over time	Slay the Spire card-reward-of-3 + skip

The anti-dominant-strategy discipline

A build system is healthy when several distinct strategies clear the game at a similar rate. Four levers keep it that way:

Multiple engines, none strictly best. Poison, crit, block-scaling, summons — each should win in the hands of a pilot who commits. If one wins with no commit, it’s dominant. Cut or nerf it.
Near-hard counters keep any single engine honest. A build with no weakness is a dominant build; give each strategy a matchup it dreads (system-counter-systems). Diversity and counters are the same problem.
Meaningful exclusivity. If you can take everything, there’s no build — just a checklist. Force trades: branch exclusivity (system-skill-trees), deck size, slot limits, opportunity cost.
Reward the synergy, not the pile. Diversity comes from parts that interact (system-status-effects combos), not from a longer list of flat +damage. Flat stacking always converges on one optimum.

The proof is the delta, not the roster. A big list of weapons proves nothing. What proves diversity is: pilot build A, it wins; pilot build B, it wins; pilot the null / flat-stack build, it loses. (FUN.md law 2, §11 draft-delta.)

Tuning levers

Lever	Does	Healthy range
Win-rate spread across builds	how even the top strategies are	tight — no build ≫ the field
Synergy multiplier	payoff of a combo’d build	big enough to reward commitment, not so big it’s mandatory
Exclusivity	how much you must give up to specialize	real trades; you can’t have it all
Floor build power	how the “no plan” run does	it loses — the null baseline (law 2)
Ramp/scaling	how builds keep pace with difficulty	multiplicative build vs superlinear threat (§6)

How it wires to Hayao

Pilot bots per build. Pure state + world.rng (FUN.md law 7) lets you script a greedy pilot for each archetype, run it, and compare win-rates. Assert the intended builds land inside a win window and the null build falls below it (FUN.md §11).
The draft delta is the direct test. Same pilot, drafting off, must lose much more (Slay the Spire’s 17→9). That single assertion catches “the build doesn’t matter” and “one build dominates” at once.
Synergies are pure status/state — no special API; it’s your data (grep docs/API.md). Reward drops via weightedPick/pickEntry through world.rng keep the offer fair and replayable (system-reward-schedules).
Reference: anchor-slay-the-spire DNA (draft-of-3 + skip, archetype engines).

Fails when…

A dominant strategy. One build ≫ the field; every run converges on it, the build screen is a lookup. The single most common diversity failure.
Flat stacking. +damage on +damage always has one optimum; no interaction, no identity (pattern-emergence is absent).
No exclusivity. You take everything → there’s no build, just accumulation.
Trap options. Choices that are always wrong aren’t diversity — they’re padding. Every offered part should win somewhere.
Diversity that doesn’t survive scaling. Builds that all work at easy but only one keeps pace with the ramp (§6) — that’s a dominant build in slow motion.

Verify

FUN.md §11 — greedy pilot per build in the win window; never-draft/null build below it; the draft delta.
FUN.md law 2 — each viable build beats the null build by a margin.
FUN.md §6 — builds keep pace with a superlinear ramp (for horde/survivor builds).
Determinism: golden hash of a scripted run per build.

Composes with

system-status-effects — the interacting parts that make synergy engines.
system-counter-systems — near-hard counters keep any single build honest.
system-skill-trees — branch exclusivity is a primary diversity source.
system-reward-schedules — how build parts are offered (draft-of-N, drops).
system-meta-progression — persistent unlocks widen the build space over time.