Build a 2D platformer: run/jump control with coyote time, jump buffering, and variable jump height, plus tiled levels and hazards. Use for a platformer or Mario/Celeste-like, or tuning jump feel.

Platformer A playbook for 2D platformers — the run/jump controller "feel", level structure, hazards, and goals. This is a compositional skill: it wires an engine movement skill, a tilemap skill, and design skills into a working game. It does not re teach physics or tilemaps; it tells you what to build and how to make jumping feel good. When to use Use when building a side scrolling or single screen platformer, a "Mario like" / "Celeste like", or any game whose core verb is jump between surfaces . Use when a jump feels floaty, unresponsive, or "unfair" and you need feel fixes (coyote time, jump buffering, variable height, corner correction). When not to use: top down movement with no gravity → use the engine movement skill directly. 3D first person traversal → fps shooter . Grid/turn movement → roguelike . For the raw kinematic body API, use godot 2d movement (or your engine's controller skill). Core loop Observe a gap/hazard → commit to a jump or move → land safely (or die) → reach the next checkpoint/goal. A platformer lives or dies on the moment to moment feel of that single jump, repeated thousands of times. Tighten the controller first; everything else is content. Must have systems 1. Run/jump controller — horizontal accel/decel, gravity, jump, with the feel aids below. 2. Solid + one way collision — ground, walls, and "jump through" platforms. 3. Level geometry — a tilemap or hand placed colliders; the playable space. 4. Hazards + death/respawn — spikes, pits, enemies; reset to the last checkpoint. 5. Checkpoints / level goal — progress markers and a win condition (flag, door, exit). 6. Camera — follows the player with a deadzone and look ahead, clamped to level bounds. 7. Juice — landing dust, squash/stretch, hit stop, sound. Cheap, huge feel payoff. Design knobs (make the jump feel right) Tune these by outcome (height in tiles, time to apex in seconds), not by raw numbers. Knob Effect Sane starting point Max jump height reach 3–4 tiles Time to apex "weight"/snappiness 0.30–0.40 s Fall gravity multiplier snappy, non floaty fall 1.5–2.0× rise gravity Coyote time jump just after leaving a ledge 0.08–0.12 s (~5–7 frames @60) Jump buffer press just before landing still jumps 0.10–0.15 s Variable jump cut tap = short hop, hold = full cut upward velocity ×0.4–0.5 on release Apex hang brief float at the top for air control reduce gravity ×0.5 near vy <threshold Ground accel / friction responsiveness vs. ice reach top speed in 0.05–0.1 s Corner correction nudge past a ledge clipped by 1–2 px nudge up to ~4 px sideways Wall slide / wall jump controlled descent and kick off wall grace, kick/steering lock, air jump refresh policy; see refs §9 Derive gravity and jump velocity from the feel values rather than guessing — see Pattern 1. Patterns 1. Solve jump physics from height + time (not magic numbers) 2. Coyote time + jump buffer + variable height (the feel core) For wall or air jumps, replace this simple jump resolver with the unified resolver in refs §9; keep variable height and gravity integration only once per tick. 3. One way platforms Solid from above, pass through from below. Use the engine's flag rather than collision math: Godot CollisionShape2D.one way collision (or the one way option on a TileSet collision polygon), Unity a PlatformEffector2D with Use One Way on a collider set to be used by the effector, Phaser Arcade platform.body.checkCollision.down = false (plus left / right for thin ledges). Let the player drop through by ignoring that platform for ~0.1–0.2 s when they hold Down + Jump (refs §5). Pitfalls / failure modes Per frame movement not scaled by dt → speed changes with frame rate. Every velocity integration and timer must use dt . (See physics tuning .) Jump height differs between machines → the jump runs on a variable render dt . Simple per step integration lands a few percent short of the designed height, by a different amount at each frame rate. Run the controller on the fixed physics tick (Godot physics process , Unity FixedUpdate ) or use the half step update in refs §1. Player is flung off or doubles speed leaving a moving platform → platform velocity added twice. Godot's CharacterBody2D already carries the body and adds the platform's velocity on leave ( platform on leave ); don't add it again in script (refs §6). Floaty jumps → symmetric gravity. Make fall gravity heavier than rise gravity. "The jump didn't register" → no input buffering. Buffer presses for ~0.1 s before landing. "I fell off and couldn't jump" → no coyote time. Allow a jump for ~0.1 s after leaving ground. Wall jump overrides a ground jump or consumes the double jump → resolve one buffered press in ground/coyote → wall → air order, with an explicit air jump refresh policy (refs §9). Sticking to walls / catching on tile seams → use a single capsule/box collider, not per tile colliders, and add corner correction. Tunneling through floors at high speed → enable continuous collision / smaller fixed timestep for fast bodies (see physics tuning ). Camera snaps and induces nausea → smooth/lerp the follow, add a deadzone, clamp to bounds. Difficulty wall from bad teaching → introduce one mechanic per area before combining them. Composition (build it from these skills) Controller body: godot 2d movement (Godot CharacterBody2D ); for other engines use the engine core + physics skill ( unity physics , phaser arcade physics , pygame core ). Levels: godot tilemap / unity tilemap 2d for geometry; level design for layout, pacing, and teaching order. Feel/physics: physics tuning for timestep, CCD, and stability. Input: input systems for buffering, rebinding, and gamepad support. Polish: audio design for SFX/music; the engine animation skill for squash/stretch. Process: prototype fast to greybox the controller before building content. References For jump math derivation, wall slide/jump, a full feel tuning table, corner correction, moving/one way platforms, and camera follow, read references/feel tuning.md .