What it is. A layer of optional goals (achievements) and social ranking (leaderboards) bolted onto play. Achievements name skilful or thorough behaviour and reward it with a badge; leaderboards sort players against each other or the world.

Player fantasy / why it’s fun. “I did the hard thing, and there’s proof.” Achievements convert diffuse mastery into legible status; leaderboards give it an audience. The pull is extrinsic — it works only when it points at play that was already worth doing.

When to use / when NOT

Use when:

• Your core loop has depth players won’t exhaust on the golden path — extra goals surface it. See pattern-mastery-and-flow.
• You want a long tail: reasons to return after the credits. Pairs with system-meta-progression, system-prestige-and-newgame-plus.
• Play is comparable — a clean score, a clock, a run — so ranking is meaningful. See system-coop-and-competition.

Do NOT use when:

• The reward has to manufacture motivation the game lacks. A badge cannot rescue a boring loop; fix the loop first (process-core-loop).
• Goals would drag players off the fun path onto a tedious optimum — the antipattern-boring-optimal trap.
• Scores aren’t comparable (heavy build variance, uncapped RNG) and a board would just rank luck. See antipattern-rng-frustration.

Variants

Tuning levers

• Goal legibility. State the target crisply (beat the boss without dashing) or hide it deliberately (see twist below). Ambiguity that forces a wiki is antipattern-guess-the-designer.
• Reward. Cosmetic-only (a badge) keeps play honest; power rewards drag players onto the grind. If earning it changes the meta, you’ve built system-reward-schedules, not an achievement — treat it as such.
• Effort curve. Spread from trivial (first kill) to brutal (100% no-death) so every skill tier has a next rung. A wall of only-brutal reads as antipattern-grind-wall.
• Anti-cheat. Boards are worthless if the top is fake. Prefer replay verification (re-simulate the seed + inputs) over trusting a submitted number.
• Board freshness. Rolling windows (this week, this season — see system-live-ops-and-seasons) keep the #1 slot contestable; an all-time board calcifies.
• Failure legibility. Missable achievements need a warning or a mercy path; a permanent lockout for an unmarked choice is antipattern-backtracking-tax.

Twist seams

• Leaderboard but everyone races the same daily seed (constraint) — remove luck as an excuse. One seed, one day, global; the run is now a pure test of decisions, and coffee-break replay chatter emerges (anchor-spelunky daily, anchor-slay-the-spire daily climb). Fairness demands a fixed close time and replay proof.
• Achievements but the game hides they exist until earned (structure) — no list to grind, no spoilers. Each pop is a genuine surprise that retroactively names what you just did — the anchor-outer-wilds and anchor-return-of-the-obra-dinn register-of-discovery feel. See pattern-surprise-and-delight. Cost: no signposting, so tie unlocks to natural play, never to obscure inputs.

How it wires to Hayao

• Achievement checks are pure predicates over run state. Fold them into your end-of-run summary as functions of the recorded outcome (deaths, time, items) — the same probe surface tests already read. No new subsystem; a badge is a boolean.
• Determinism makes boards possible. Because the sim is seed-driven and reproducible, a leaderboard entry can be (seed, input-log) and re-simulated to verify the score — that’s your anti-cheat, for free, from the same replay tooling the anchor-spelunky-style daily needs.
• Daily seed = one seed, one calendar day. Derive it from the date so every player shares a run; keep all randomness on the deterministic RNG so identical inputs give identical outcomes.
• Chrome is DOM, the badge pop is cosmetic. The achievement list, the board table, the toast — menu-and-overlay furniture, kept out of sim state; see the logic/view split in examples/sokoban/. For the toast’s juice, pattern-juice-choreography.

Fails when…

• It rewards the tedious over the fun, pulling players onto a joyless optimum — antipattern-boring-optimal.
• The board’s top is a solved, cheated, or luck-decided slot no honest player can touch — antipattern-solved-metagame, antipattern-rng-frustration.
• 100%-ing becomes an obligation chore instead of an invitation — antipattern-grind-wall, antipattern-content-desert.
• Targets are unguessable without a guide — antipattern-guess-the-designer.

Verify

Assert achievement predicates fire exactly on the intended run states, and that a submitted (seed, inputs) re-simulates to the claimed score, per docs/VERIFICATION.md. Design the goals here; prove they trigger — and only then — there.