🟢 Xbox2001BungieVERY HARD

Halo: Combat Evolved rebuild deck

VERY HARD

A blackboard and a behaviour tree buy legible squad AI in a weekend, which leaves the part Bungie actually spent ninety team-years on: every arena tuned until each fight is thirty seconds of fun.

You will get a good prototype. The product is what comes after.

Halo is on this list as the definitive AI project. One prompt gives you enemies that shoot at you; getting them to make decisions you can read from across an arena is the whole 90 team-years. What is remarkable is how far a good prompt gets — a blackboard plus a behaviour tree produces genuinely legible squad behaviour in a weekend, which would have been a research result in 1999.

Difficulty: VERY HARD · 4 of 5
First playable: A project
The original: 90 team-years
Released: 2001 · Xbox
Genre: FPS

The one-shot build prompt

Build a first-person shooter sandbox prototype focused on enemy AI. three.js, one arena, three enemy types.

Requirements:
- The AI is the project. Implement a behaviour tree per enemy with these layers, in priority order: self-preservation (retreat when shields drop), squad coordination (do not all flank the same side), positioning (seek cover with line of sight to the player), and engagement (fire in bursts with reload gaps). Enemies must visibly make decisions.
- Three enemy archetypes that combine into encounters: a weak swarm unit that panics and flees when its leader dies, a shielded mid-tier that advances behind cover, and a heavy that forces the player to reposition. The interplay between them is the encounter design.
- Squad state shared through a blackboard: last known player position, which cover points are claimed, who is currently suppressing. Without a blackboard you get three individuals, not a squad.
- Player: recharging shields plus a small health pool, a two-weapon limit with a swap, grenades on a separate button, and melee. The two-weapon limit is what makes the sandbox work — never add a third slot.
- Weapons with genuinely different roles: hitscan precision rifle, a projectile with travel time and arc, a fast-fire bullet-hose with recoil bloom. Every weapon is good against something and bad against something.
- Encounter arena built as a bowl with layered cover, multiple approaches, and vertical positions — never a corridor.
- Feel: shield-break flare, hit markers, weapon recoil with recovery, and enemy reaction animations that read at distance.

Definition of done: I kill the squad leader and the remaining enemies panic, and I laugh.

Before you start🧰 The toolkit — models, MCP servers, art and 3D

What you lose

The enemy AI, which is still one of the best-documented and least-replicated systems in games
The "30 seconds of fun" encounter design, tuned across every arena in the game
Marty O'Donnell's score and the sound design of every weapon
Two-weapon-limit balance across a sandbox that has been argued about for 25 years

What to steal

A squad blackboard with claimed cover points

Enemies sharing one blackboard look like a squad; enemies each thinking alone look like five copies of the same enemy however good the individual behaviour is. Claimed cover points alone buy most of the effect, and they take an afternoon.

ScopeA weekend— build just this, not the game

Build a top-down squad AI sandbox as a single self-contained HTML file. Canvas 2D, no build step. The AI is the whole project; the player is a dot that moves and shoots.

- One arena of walls and scattered cover points. Five enemies.
- Each enemy runs a behaviour tree evaluated in priority order: retreat when hurt, coordinate with the squad, take a cover point with line of sight to the player, then fire in bursts with reload gaps.
- All shared state lives in one blackboard object: last known player position, which cover points are claimed, who is suppressing, who is flanking which side. Cover is claimed and released, so two units never take the same rock and never flank the same side at once.
- One unit is the leader. Kill it and the rest drop into a panicked behaviour for three seconds before regrouping.
- Debug view on a key: draw each unit's current node name above it, its claimed cover point, and its line of sight.

Definition of done: with the debug view off, I can tell from movement alone that they are flanking me.

Make it different

Not a clone — Halo: Combat Evolved 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. 24,360 ways to land.

Matchday One Run

Halo: Combat Evolved, but a roguelike run instead of a campaign, set in pro sports. Rendered in manga screentone.

Themepro sports

Anglea roguelike run instead of a campaign

Lookmanga screentone

Build a browser game called "Matchday One Run".

The pitch in one line: a fps in the spirit of Halo: Combat Evolved, but a roguelike run instead of a campaign, set in pro sports.

WHAT THIS IS
Take the SHAPE of Halo: Combat Evolved — 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 roguelike run instead of a campaign. Twenty to forty minutes, procedurally assembled from hand-authored chunks, permadeath, and a meta-progression drip. Replaces authored content volume with combinatorics.
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
Pro sports. Rules of a real sport as the combat system, a crowd that reacts, and a season structure even if you only ship one match.
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
Manga screentone. Black ink linework, tone sheets for shade, speed lines, and onomatopoeia bursts as diegetic UI.

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.

Prior art — read before you build

Half the time one of these already does what you wanted, and the other half it saves you a week of solving a problem someone documented in 1997.

Did you build it?

0Share on X

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 90 team-years to the counter on the homepage.

Then try these

Or roll something nobody has built yet →

Questions

How hard is Halo: Combat Evolved to rebuild with an AI agent?

Yes — every game is buildable at some scope. The question is how hard, and Halo: Combat Evolved is VERY HARD (4 of 5). You will get a good prototype. The product is what comes after. A blackboard and a behaviour tree buy legible squad AI in a weekend, which leaves the part Bungie actually spent ninety team-years on: every arena tuned until each fight is thirty seconds of fun. Reckon on a project to something you can actually play — not to something that matches the 90 team-years Bungie spent.

What makes Halo: Combat Evolved hard to rebuild?

A blackboard and a behaviour tree buy legible squad AI in a weekend, which leaves the part Bungie actually spent ninety team-years on: every arena tuned until each fight is thirty seconds of fun. 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 a squad blackboard with claimed cover points — a weekend of work.

How long does it take to build a Halo: Combat Evolved clone?

Wrong question, and it is worth saying why. Nobody rebuilds Halo: Combat Evolved — the original took Bungie on the order of 90 team-years, released in 2001 on Xbox. What you can do is reach something playable and genuinely yours in about a project, 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 Halo: Combat Evolved?

The enemy AI, which is still one of the best-documented and least-replicated systems in games. The "30 seconds of fun" encounter design, tuned across every arena in the game. Marty O'Donnell's score and the sound design of every weapon. 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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