Composition — Assembling the Design

What it is. The assembly step. Take the anchor (the X), lay down its genre template, and bolt on the systems that genre implies — progression, economy, combat, factions. Composition is sourcing the parts; process-the-twist is the bend you apply while you assemble.

Why it’s fun. You don’t re-derive what a roguelite knows about meta-progression; you compose it, pre-solved, and spend your invention on the twist. The craft here is picking the right parts and making a blend cohere rather than collide.

The step

Anchor + pillars → a composed design: one genre template, N systems, a coherent whole. Every included part must pass the process-pillars filter and serve the loop stack (process-core-loop).

Inputs → outputs

The assembly

1. Anchor → genre spine. The anchor names the genre. Pull the deep template from 20-genres/ — its pillars, loop stack, and essential systems. This is your skeleton; you’re not starting from zero.
2. Genre → implied systems. Every genre implies systems. A roguelite implies meta-progression and procgen; an RTS implies rosters, economy, and asymmetry. Use the checklist below.
3. Twist → added/swapped system. The twist usually is a system swap or add (Loop Hero adds placement + a deck to auto-combat). Slot it in.
4. Filter every system. Score each against the pillars. Include only what serves one. When in doubt, cut — an unverified system is presumed broken.

Which systems does this genre imply?

A starting checklist. Presence isn’t mandatory — but decide on each, don’t forget it.

Two systems on that last row are always on: readability (JUDGE hook) and juice choreography (JUICE hook). Skip nothing there.

Genre-blend rules

Most interesting games are blends — two or more genres under one loop (Loop Hero = auto-battler + deckbuilder + placement; rhythm = roguelike + input legality). The rule that keeps a blend from collapsing:

Satisfy every parent genre’s verify pattern. FUN.md’s closing note is law: “If the genre is a blend, satisfy every parent genre’s verify pattern — genres compose (rhythm = roguelike + input legality; Peggle = physics + aim search).” A blend is not an average of two verify suites; it is the union of them.

Practically:

1. List the parents. Name each genre in the blend and its FUN.md section.
2. Union the verify patterns. A physics-arcade + deckbuilder owes both the swept-collision/energy invariant (FUN.md §19) and the draft-delta + win-rate window (FUN.md §11). Neither is optional.
3. Find the seam. Where two systems meet is where blends break — the moment a card modifies a physics shot, both models must stay honest. Name that seam and plan a proof for it specifically.
4. Pick the dominant parent. One genre owns the moment verb; the others modify. The dominant one’s loop stack is the spine; the others graft on.

Worked example

Intent: “a tower defense where the towers are a deck you draft each wave.” Pillars: (1) build decisions that matter, (2) drafts with teeth, (3) the range ring is the UI. X = tower defense × deckbuilder blend.

Composition:

• Spine: genre-tower-defense owns the moment verb (place a tower). FUN.md §8 is the primary verify pattern.
• Grafted parent: genre-deckbuilder supplies the draft-of-3 per wave. FUN.md §11’s draft-delta + win-rate window applies to the tower draft.
• Implied systems: system-economy (gold faucet from kills), system-counter-systems (near-hard tower↔enemy counters — §8 demands it), system-encounter-design (wave composition), system-reward-schedules (the draft is the reward).
• The seam: a drafted tower must respect coverage geometry (§8’s range × lane chord) and the draft must have teeth (§11’s delta). The seam-proof: a mixed drafted build survives 10/10 while a mono-draft (bigger budget) fails and never-drafting loses by a margin. Both parents, one scenario.
• Cut: a proposed crafting system — serves no pillar, adds a third verify suite for no fantasy gain. Out.

Traps

• Averaging verify suites. A blend owes the union, not the intersection. Two parents = both proofs, in full.
• Two dominant parents. If two genres fight for the moment verb, the game has no center. Pick one spine; the rest modify it.
• Ignoring the seam. Blends break where systems touch. The seam needs its own named proof, not a hope that both halves compose cleanly.
• System sprawl. Every system you add is a verify suite you owe. Compose the fewest systems that serve the pillars; each extra one is scope you must prove.
• Composing from the corpus. Don’t survey examples/ for which systems to bolt on (see CLAUDE.md). Decide from the mechanic and the pillars; borrow structure, not a menu.

Composes with

• process-the-twist — the twist is chosen during composition; it’s the creative bend on the parts you’re assembling.
• process-pillars — the filter that decides which systems are in.
• process-core-loop — the systems fill the loop stack’s layers.
• process-refine-and-handoff — the composed system list becomes the list of verify suites you owe.

See also

• design/FUN.md Part 2 + closing note — the per-genre verify patterns and the blend law you must satisfy for every parent.
• 20-genres/ · 30-systems/ — the parts bin you assemble from.
• examples/ — convention references for how a composed design wires state/view, not an idea menu (per AGENTS.md).