What it is. A space of consistent, interacting systems and a small verb toolkit, arranged so any obstacle admits several valid solutions the designer never scripted. The author builds the physics, not the path.

Player fantasy / why it’s fun. This was my plan. You read a situation, combine tools nobody promised would combine, and the world honors it — the win is authored by you, not handed to you.

Pillars (exactly 3)

1. Systemic consistency. Fire spreads, water conducts, guards hear noise, gas ignites — everywhere, always, no exceptions for the “real” puzzle. The rule that holds once must hold every time or the fantasy collapses into guesswork (antipattern-guess-the-designer).
2. Player authorship. Many verbs (move / see / hide / manipulate / possess) with wide overlap. Depth comes from combination, not from a longer list (system-build-diversity, pattern-emergence).
3. Meaningful stealth-or-force choice. The core tension: sneak past, talk around, or fight through — each a real, costed lane, none the “correct” one (pattern-meaningful-choice, pattern-risk-reward).

The loop stack

Essential systems

• Honest AI. Guards perceive by real senses — sight cones, sound falloff, corpse/light discovery — and their state is readable on the actor. If the player can’t infer why a guard reacted, the sim is broken. See system-enemy-ai, system-telegraphs, and the genre-stealth detection model.
• Interacting hazards. Fire, water, electricity, gas, gravity, light — each a system that touches the others, not decoration. See system-hazards-and-environment, system-status-effects.
• A toolkit. Traversal + manipulation verbs that compose: mechanic-possess, mechanic-teleport, mechanic-grapple, mechanic-throw, mechanic-time-stop. Pick verbs that multiply each other.
• Legible spaces. Level geometry that advertises its options — vents, high ledges, water, cover — so the sandbox is seen, not memorized. See system-map-and-navigation, world-level-as-story, pattern-readability.
• Consequence tracking. The world remembers your body count and alarms and reflects it (system-quests-and-objectives, the Chaos system in Dishonored).

The hard part is legibility. A deep system nobody can read is antipattern-false-depth; build systems that show their state before you make them deep.

Content & difficulty model

• Author the sandbox, not the solution. Design each space as a set of affordances; verify at least three intended routes exist, then let players find the fourth. Solver-proof reachability, never a single canonical path.
• Difficulty is denial, not damage. Harder = fewer verbs available, tighter patrols, deadlier discovery — not fatter health bars. Tune via system-difficulty-and-dda, system-encounter-design.
• Onboard the systems, not the story. Teach fire+water, sight+sound in a safe first space where consequences are cheap (system-onboarding); one clean interaction beats a wall of tooltips (antipattern-endless-tutorial).
• Reward exploration and restraint both. Ghost/pacifist runs and murder runs each need payoffs, or one lane becomes the antipattern-boring-optimal.
• Density over sprawl. A few hand-built, deeply reactive spaces beat a large map of thin ones (antipattern-content-desert).

Signature-mechanic seeds

• Imm-sim but non-lethal only (constraint). Ban killing; every verb must resolve to sleep, distract, trap, or reroute. The toolkit’s reach now defines difficulty, and the moral fantasy sharpens — cf. Dishonored’s low-chaos path made mandatory.
• Imm-sim but the systems reset each loop (structure). The mission repeats like Outer Wilds; hazards, patrols, and locks reset, but your knowledge persists. The upgrade tree is what-you-learned, not what-you-bought — see anchor-outer-wilds, mechanic-rewind.
• Imm-sim but the tools are enemies (inversion). Every verb is a possessed foe — you have no innate powers, only bodies you steal (mechanic-possess, mechanic-clone); the roster of nearby enemies is your inventory.
• Imm-sim but one shared meter (economy). Traversal, powers, and healing all draw one resource (system-resource-loops, system-economy); every teleport is a healing potion you didn’t drink.
• Imm-sim but the AI writes the story (systemic narrative). A nemesis system remembers who beat you and escalates them (anchor-shadow-of-mordor, recipe-colony-nemesis) — the antagonist is emergent, not scripted.

Common pitfalls

• antipattern-guess-the-designer — the intended solution masquerades as the only one; players poke and get punished. Fix: honor every solution the systems permit.
• antipattern-false-depth — systems interact in theory but their state is unreadable, so nobody discovers it. Fix: legibility before depth.
• antipattern-fake-choice — three routes that all funnel to the same scripted beat. Fix: let outcomes actually diverge.
• antipattern-boring-optimal — one verb (or the murder lane) dominates because it’s strictly safer/faster. Fix: cost every lane; reward the hard ones.
• antipattern-feature-soup — twenty verbs, none composing. Fix: fewer verbs, higher overlap (antipattern-second-system).
• antipattern-input-lie — a guard “should” have heard you but didn’t, or did unfairly. Fix: perception must match its telegraph exactly.

Anchors

• anchor-dishonored — the reference: sight/sound AI, a verb toolkit (Blink, Possession, Windblast), interacting hazards, and Chaos as consequence. Study how each power multiplies the others.
• anchor-outer-wilds — the knowledge-is-progress, systems-reset variant; proof that the toolkit can be understanding instead of items.
• anchor-shadow-of-mordor — the nemesis system as emergent, remembered narrative.

Neighbors worth raiding: genre-stealth (the detection core), genre-metroidvania (verb-gated space), genre-action-adventure (the traversal+combat frame).

Verify

Prove the systems, not the vibe. Reachability of every intended route belongs in a pure solver; the stealth detection and consequence model verify against design/FUN.md#5-·-stealth. Feel and legibility are proven in JUICE/JUDGE, not asserted here.