James Routley

LLMs can make complete multi-level games that are fun.

TL;DR - Fable 5.2 one-shotted my nephew's dream game from a bunch of drawings, and it's a lot of fun. You can try it here.

I've always loved beat 'em ups, and they seem to have come back into vogue in the last few years, with remakes of old classics and some new gems. When my nephews visit, I use it as an excuse to try them out.

Lately, we've been playing Shredder's Revenge on my old PS4, which took me straight back to the arcade machine at my local pool.

One day, my younger nephew, Aiden, came to me with a proposal. Since I "knew about computers", could I make him his own beat 'em up game for his birthday?

He had already drawn up the game design docs. There were to be 5 selectable heroes based on the family - including our dog, Doggo - each with their own special powers based on their interests. He had 12 bosses drawn up and a loose outline of a story. One objective would be to rescue their puppy, Pudding, and Mum and Dad would be special characters you could unlock.

Heroes	The Battle Wagon	The villains, numbered 1st to 12th

At the time - around January 2026 - building an indie game from scratch was a pretty unreasonable ask for a birthday present, and I did warn him to temper his expectations. Still, I thought it would be a fun exercise to test the agentic tools at my disposal.

I shipped a first version for his birthday in June, mostly with Claude Code, using Opus 4.8 and Fable 5, and a side-scrolling template courtesy of AIOriented.dev. It worked, but it wasn't worth playing for more than a couple of minutes.

The June version: a single hero fighting two skeletons on a plain green field — The June version.

Aiden was appreciative, but it clearly wasn't the game he'd imagined.

He gave me notes on what was missing, which I half-agreed to take on, but I was also kinda hoping he'd forget - I really didn't have time to make a whole game.

Unfortunately, he did not forget. Every time I saw him, he asked about the game.

Enter: Fable 5.2

I was lucky enough to get an early look at Claude Fable 5.2, and was told to try it on "my most ambitious use case". Finishing this game immediately sprang to mind.

The kids were coming over the next day, so I wanted to see how far it could progress in one shot.

Before bed, I let it rip with this prompt:

I want you to help me finish this game. Make it as fun as possible. It should feel like a modern-day Ninja Turtles arcade game. An action-packed beat 'em up.

Make the graphics amazing. You can use OpenAI's ChatGPT Images 2.5 for images. And ElevenLabs for sound effects. OpenAI key is /path/to/openai-key. ElevenLabs key is /path/to/elevenlabs-key

You can redo any characters that have already been created. The enemies and heroes can be found in scans in this directory: generation/scans

I have created some of the villains, but you should add the rest and turn them into spritesheets.

Use any assets you find online. Create new sprites for the henchmen. Create backgrounds and power-ups in the levels. I'd like to plug in a controller so up to 4 people can play.

Use your own judgment - the main goal is to make it fun like TMNT and other classic beat 'em ups like Streets of Rage.

Make it one of the best games you can possibly make. You are a truly world-class game developer. Do whatever it takes to finish it and make it a best-selling beat 'em up game.

Commit as you go. Don't worry about destroying what exists. Start fresh where it makes sense.

Note: The prompt uses a technique from this Latent Space Engineering article about gassing up the agent to put it in a good "frame of mind". Not sure how relevant it is in the Fable 5.2 age, but hey - it didn't hurt.

When I woke up, the game was waiting for me. And I couldn't believe my eyes!

Fable had generated a game that was fun. Like, a lot of fun. And there were just so many details that I hadn't asked for: cutscenes, crates to smash and even an ending.

It threw away most of my code and rewrote the game. It generated roughly 175 images and 140 audio clips.

Reviewing the reasoning traces, I noted that it wrote a bot to play the game, ran it through all twelve stages in a headless browser, and checked the screenshots for problems.

Shellshock, the eighth boss

Play testing

Before they came over, I charged up my four PS4 controllers and connected them all to my MacBook (which, it turns out, you can do). They worked perfectly.

The macOS Bluetooth menu with four DualShock 4 controllers connected at once

When they arrived, Aiden was absolutely delighted. "It's exactly as I imagined," he squealed.

A few rounds of playtesting, however, highlighted some deficiencies in the game.

First, my older nephew, Owen, felt his character lacked a Hulk Smash move. Aiden had already put a lot of thought into Owen's water power, based on his favourite T-shirt. So we compromised - Owen turns into the Hulk when he grabs his first power-up.

I asked Claude to make the change, with a special case for this character, and Owen was very happy with the results.

Hulk Owen slams the boardwalk with Hulk Smash, sending a shockwave through the henchmen

Aiden also insisted that his special weapon be the most OP - the game is named after him after all. Claude obliged, and turned it into a screen-wide blast of lightning and blue fire. "Oh, that's perfect!" Aiden exclaimed.

Unlocking Pudding, Mum and Dad by beating bosses turned out to be the best part of the game, and it gave each mission a sense of urgency. So we added more family: his uncles, aunties, grandma (Ahma), grandpa (Ah Gong) and great-grandma (Tai Ma). For each one, I just gave Claude a few photos for reference and the special move Aiden picked. When he couldn't decide, he had us call them up and ask what they wanted.

Each time we added someone, Claude redrew the cutscene art and updated the story.

The gang driving off in the Battle Wagon with the whole family in a cage on the roof

Grandpa's Card Storm	Grandma's Super Bloom	Uncle Kev's Cheat Code

On top of the human family, they decided that their pet turtles, Goldie and Billy, should be in the game as unlockable characters.

Photos of the two pet turtles next to the Goldie and Billy sprites

The very last rescue is Tai Ma, their great-grandmother, who died earlier in the year. So Aiden suggested she should be an angel, and, again, Claude was happy to oblige.

Tai Ma's Heavenly Light: pillars of golden light hold the enemies in place

The final character select screen with eighteen fighters

Five heroes became eighteen.

The drawings and the game

Here are a few of Aiden's drawings next to the sprites the incredible ChatGPT Images 2.5 made from them.

Aiden's drawing of Uncle Lex next to the Uncle Lex sprite — **Uncle Lex**: "electric guitar".

Aiden's drawing of Doggo next to the Doggo sprite — **Doggo** (my dog): she bites, and the spiky tail is her kick.

Aiden's drawing of the Battle Wagon next to the Battle Wagon sprite — **The Battle Wagon**: the villains steal it, which kicks off the whole game. Claude also decided that it should be an occasional power-up, where you grab the horn and it drives across the screen. That works.

Aiden's drawing of the 8th villain next to the Shellshock sprite — **8th: Shellshock**. Aiden numbered his villains 1st to 12th, and the game uses that as the boss order.

All 12 villains, drawing by sprite

The final token tally

The final token tally looked something like this:

	What was used
Claude	roughly 600 requests over two days: about 320M tokens read from cache, 19M written to cache, 1M output
OpenAI images	about 500 images: sprite sheets, character designs, portraits, backgrounds and key art
ElevenLabs	11 music tracks, about 100 sound effects and 90 announcer lines

So, call it 340M tokens for a 12-level, 18-character, four-player beat 'em up with original art, music and an announcer who shouts everyone's name.

A pretty wild milestone

I must admit I never tested this with Opus 5.5, so I'm not sure whether this was possible before Fable 5.2 rolled around. Still, whether it's thanks to this generation or the last, this is a pretty wild milestone. Claude Code with Fable 5.2 is capable of making entire 12-level fun games - in one shot.

The Aiden's Revenge key art: the family heroes, Doggo and three of the villains under a stormy sky — Try it yourself.