🖥️ PC2015Toby FoxVERY HARDUndertale rebuild deck
VERY HARD
An agent assembles the bullet-hell and the spare flag before dinner, which is precisely the problem, because everything anyone stayed for is Toby Fox's writing and comic timing.
You will get a good prototype. The product is what comes after.
Technically this is a modest state machine bolted to a small bullet-hell, and an agent will assemble it before dinner. That ease is exactly why it is a no. Papers, Please survives losing its script because checking documents is a game on its own; a generic bullet-hell with a spare button is not, so everything you can actually build here is the part nobody stayed for. Data-drive the patterns so you can iterate on the only thing worth authoring, then accept that the writing is a separate skill. Agents produce RPG dialogue that reads like a pitch deck for a fantasy novel; keep one away from your script.
- Difficulty
- VERY HARD · 4 of 5
- First playable
- A weekend
- The original
- 3 team-years
- Released
- 2015 · PC
- Genre
- Bullet Hell RPG
Build a turn-based RPG where every enemy attack is a short bullet-hell phase and fights can be ended without violence. Single self-contained HTML file, Canvas 2D, Web Audio, no build step.
Requirements:
- Turn loop: the player picks FIGHT, TALK, ITEM or SPARE, then the enemy attack phase runs for 5-8 seconds inside a rectangular box the player's token cannot leave.
- The spare flag is load-bearing. Each enemy carries hidden state that only specific TALK choices change. SPARE ends the fight only once that state is satisfied, and refuses until then. Dialogue lines and attack patterns are keyed to that same state, so behaving differently produces a visibly different fight rather than a different ending screen.
- Bullet patterns are timeline data, not code: a list of {t, spawn, position, velocity, lifetime, sprite} entries driven by one scheduler. Every pattern lives in JSON.
- The player hitbox is 6x6, deliberately smaller than the drawn sprite. One second of invulnerability with a 6Hz flicker after a hit.
- The box resizes between phases over 200ms ease-in-out, and pushes the token inside if it shrinks underneath it.
- FIGHT is a cursor sweeping across a bar; damage scales with distance from centre, dead centre crits.
Definition of done: I can finish the same encounter two ways, dropping the enemy to zero HP or TALKing correctly twice and sparing it, and both the dialogue and the bullet pattern differ on the second path.- Toby Fox's writing and comic timing, which is not a feature of the game, it is the game
- A soundtrack people who never played it can hum
- Two full routes hidden behind how you choose to behave, each rewriting the other
- Meta-tricks that only work once, and only on a fanbase that did not see them coming
one timing bar every action routes through
A menu click has no skill ceiling; the same click gated behind a 300ms timing window puts the player's hands back into a turn-based system. Write it once as a widget that returns a number between 0 and 1 and every verb in your game can borrow it, which is a far better use of an evening than another combat formula.
ScopeAn evening— build just this, not the game
Build a reusable timing skill-check as a runnable toy. Single self-contained HTML file, Canvas 2D, no build step. - One widget: a cursor sweeps a horizontal bar and, on keypress, returns a quality value from 0 to 1 based on distance from a target zone. Drive it from elapsed milliseconds, never frame count, so it behaves identically at 30 and 144fps. - Three consumers of the same widget prove it is generic: an attack where damage scales with quality, a dodge where above 0.8 avoids all damage, and an escape where quality sets the probability. - Tunable per call: sweep speed, target width, a narrow crit zone, and whether the cursor wraps or bounces. - Bias the crit zone a few milliseconds early to absorb input latency. Keep the raw value internally, show the player a coarse band. - Ramp: each success speeds the sweep 8% and narrows the target 5%. Definition of done: one function call drives all three actions, and an on-screen log shows raw quality against the band displayed.
Not a clone — Undertale re-themed and cut down to something you can finish. The angle is the important reel: it is what turns a project into a weekend. 5,880 ways to land.
Static From Above
Undertale, but a management sim of the same world, set in a cyberpunk sprawl. Rendered in isometric voxel.
Build a browser game called "Static From Above". The pitch in one line: a bullet hell rpg in the spirit of Undertale, but a management sim of the same world, set in a cyberpunk sprawl. WHAT THIS IS Take the SHAPE of Undertale — its core loop, and whatever makes that loop good — and rebuild it as your own game in a different world at a smaller scope. Use your own names, art and audio, which you want anyway: a reskin of somebody else's game is less interesting than a new one that works the same way. THE ANGLE — this is the important constraint, honour it above everything else A management sim of the same world. The player never controls a character — they set policy and watch agents with visible needs succeed or fail at it. This is what makes the project finishable. If a decision would push the scope back towards the original's, take the smaller option every time. THE THEME A cyberpunk sprawl. Permanent night and rain, neon as the only light source, and wet reflective surfaces doing most of the visual work. The theme is not a coat of paint. Let it change what the mechanics mean — a reload, a health pack and a locked door should all be things that make sense in this world and nowhere else. LOOK Isometric voxel. A 2:1 isometric projection over a voxel grid, with correct depth sorting and ambient occlusion baked at chunk boundaries. REQUIREMENTS - Runs in a browser with no build step. Canvas 2D unless the angle genuinely requires 3D, in which case three.js. - Fixed-timestep update loop with interpolated rendering, so it behaves the same at 60Hz and 144Hz. - Every tuning constant in one CONFIG object at the top, exposed as live sliders in a debug panel. You will find the feel by dragging those, not by prompting. - All content — levels, entities, balance numbers — in JSON or plain data files, never inline in the logic. - Audio generated with the Web Audio API rather than asset files. - Respect prefers-reduced-motion: keep the fades, drop the shake and the parallax. BUILD ORDER 1. The core loop with placeholder rectangles, at the reduced scope the angle demands. No theme, no art, no audio. Make it fun as rectangles first. 2. The angle's consequences. Cutting to bots, or to turn-based, or to one level changes the design rather than just shrinking it — find out how and rewrite step 1. 3. The theme, as content and data. 4. The look, applied last as a rendering layer over a game that already works. Start by writing a one-page plan: the core loop, what the angle removes and what that frees you to do properly, and what you are deliberately leaving out. Wait for me to approve it before writing code.
One count per game. No account — it is tied to a salted hash of your IP, which is not stored in a form anyone can reverse. Every build adds 3 team-years to the counter on the homepage.
Then try these
Questions
How hard is Undertale to rebuild with an AI agent?
Yes — every game is buildable at some scope. The question is how hard, and Undertale is VERY HARD (4 of 5). You will get a good prototype. The product is what comes after. An agent assembles the bullet-hell and the spare flag before dinner, which is precisely the problem, because everything anyone stayed for is Toby Fox's writing and comic timing. Reckon on a weekend to something you can actually play — not to something that matches the 3 team-years Toby Fox spent.
What makes Undertale hard to rebuild?
An agent assembles the bullet-hell and the spare flag before dinner, which is precisely the problem, because everything anyone stayed for is Toby Fox's writing and comic timing. That is why it sits at VERY HARD rather than a tier either side of it. If you want the idea without the project, the transferable part is one timing bar every action routes through — an evening of work.
How long does it take to build a Undertale clone?
Wrong question, and it is worth saying why. Nobody rebuilds Undertale — the original took Toby Fox on the order of 3 team-years, released in 2015 on PC. What you can do is reach something playable and genuinely yours in about a weekend, and then keep going for as long as it stays interesting. Any figure that claims otherwise is measuring a prototype and calling it a game.
What do I lose by building my own Undertale?
Toby Fox's writing and comic timing, which is not a feature of the game, it is the game. A soundtrack people who never played it can hum. Two full routes hidden behind how you choose to behave, each rewriting the other. Those are the parts a prompt will not hand you.
Which AI coding agent should I use to build it?
Any of Claude Code, Codex or Cursor will handle this prompt. Paste it as your first message, let the agent scaffold the project, then iterate on feel — the second, third and tenth prompts are where a game actually gets good. Work in an empty folder or a fresh git branch so you can throw it away cheaply.
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