guts/docs/GDD.md

GUTS — Game Design Document (v1, round 1)

Owner: Lane C (with F sign-off). This v1 settles the open questions from the original concept discussion; C refines numbers/encounters in-lane, but the decisions below are integrator-settled for v1.

Fantasy & tone

You are ENDO-1, a one-pilot micro-probe injected to clear a patient's digestive tract of a hostile infestation, mouth to exit. Tone: playful-gross medical sci-fi — Fantastic Voyage wonder, Star Fox arcade flow, a wink of Osmos-y biology-nerd humor. The body is not the enemy; it's the weather. Enemies are the infestation + an immune system that can't tell you're friendly.

DECISION — movement model: "flow-locked" hybrid

Neither pure rail nor pure 6DOF — the anatomy picks the mode:

• Tube mode (esophagus, intestines): peristalsis is a forward current you cannot fully fight. Base flow speed comes from the biome (world.biomeAt(s).flow); throttle gives ±40%, boost gives short +120% bursts. Full analog movement in the cross-section disc (mouse/stick aims, ship banks). You steer within the tube; the tube carries you. This is the Star Fox layer: readable, forward, fast.
• Arena mode (oral cavity, stomach, boss lairs): the same controller unlocked to free 6DOF, Descent-style, no gravity. Slower, spatial, exploratory. This is where fights and secrets breathe.
• Transitions are diegetic: sphincters are literal gates between modes.

Rationale: pure rail wastes the stomach; pure 6DOF makes the esophagus a boring corridor. The hybrid also keeps collision cheap in the 90% case (tube = radius test).

DECISION — structure: 5 levels + gates + 1 secret

Each level ends at a real anatomical valve, staged as a gate ritual or boss:

#	level	mode	signature mechanic	exit gate
1	Oral Cavity	arena (tutorial)	dodging molar crush-cycles, saliva tides	Epiglottis — timing gate: dive on the swallow
2	Esophagus	tube (speed run)	ride peristalsis rings for boost; reflux surge chase finale	Cardiac sphincter — outrun the acid wall through it
3	Stomach	arena (the acid sea)	pH as environmental damage; mucus shallows are safe lanes; churn cyclones	BOSS: Pyloric Guardian — the sphincter itself
4	Small Intestine	tube (the long maze)	villi forest occludes sightlines; bile slicks; immune hunters	MINIBOSS: Tapeworm chase → ileocecal valve
5	Large Intestine	tube→arena (gas swamps)	flammable gas pockets: shooting inside one detonates it (hurts everyone — risk/reward); darkness + your scanner light	BOSS: The Blockage — then triumphant ejection finale
S	Appendix (secret)	arena	hidden lair off the cecum, bonus loot + lore	—

Target: 6–10 min/level first playthrough, ~45 min campaign, built to replay for medals.

Player systems

• Hull (HP, pickups only) + Mucus coat (regenerating shield; drained continuously by ambient pH/enzymes — biome-dependent — and by hits). The coat is the pH mechanic: in the stomach open acid, coat drain is brutal; hugging mucus shallows pauses it.
• Weapons: primary lysozyme cannon (fast pellet stream, infinite, heat-limited); secondary antacid torpedo (limited ammo, AoE, also neutralizes an acid zone for ~10 s — the dual-use is the interesting bit).
• Boost with a short i-frame window at spend; recharges from nutrient orbs.
• Pickups: nutrient orbs (score+boost), mucin globs (coat refill), B12 cell (hull), antacid ammo, biopsy samples (3 hidden per level — the collectible).

Enemies (v1 roster — B implements behaviors, D makes them pretty later)

All emissive-coded (ART_BIBLE): hostile = hot amber/red, projectiles = white-hot, neutral flora = cyan (turns hostile if shot).

enemy	biome	behavior archetype
amylase droplet	mouth	slow floater, corrosive contact aura
bolus chunk	esophagus	tumbling debris in the flow (crush)
pepsin swarm	stomach	small fast seekers, dissolve on kill
churn cyclone	stomach	environmental vortex, flings you
macrophage	small int.	big slow hunter; grab → mash to escape; eats other corpses to grow
antibody turret (Peyer's patch)	small int.	wall-mounted, fires homing Y-shaped darts
gut flora colony	large int.	neutral biofilm; shot ⇒ angry E. coli swarm
gas vent	large int.	hazard: thrust-shove + flammable cloud

Bosses: Pyloric Guardian (armored sphincter; destroy mucosal nodes during open-cycles while dodging acid spouts, arena slowly churns), Tapeworm (tube chase; shoot segment weak-points as it coils around the canal ahead/behind), The Blockage (compacted-mass fortress with embedded turrets and gas pockets; peel it layer by layer, finale = the canal itself expels you both).

Scoring & replay

Star-Fox-style medals per level: score (kills × style multiplier, chained kills), par time, biopsy samples, damageless-gate bonus. Combo meter feeds the music layer (E). Endless "colonoscopy run" mode is V2 (see V2_IDEAS.md).

Difficulty & assists

Three difficulties scale coat-drain, enemy density, boss timing windows. Assist toggles (flow auto-center, aim magnetism) — arcade games live or die on feel accessibility.

Open for C to design in-lane (not settled)

Exact level lengths/pacing curves, encounter tables per segment, par times, pickup economy, boss phase timings, secret placement, tutorialization beats of level 1.