My Insane 30-Day Challenge: D&D on Game Boy with C 2025

Bling. That single, iconic sound. The moment a gray rectangle descended over the Nintendo logo, you knew an adventure was about to begin. For me, that sound recently became a starting pistol for the most ridiculous, sleep-deprived, and utterly joyful challenge I’ve ever set for myself: building a Dungeons & Dragons-style RPG for the original Game Boy. In 30 days. Using modern C.

Some people bake sourdough. Some run marathons. I, apparently, choose to wrestle with 8-bit assembly and a 4.19 MHz processor. Welcome to my insane 30-day challenge.

The Genesis of a Mad Idea

The idea sparked during a late-night session of Baldur’s Gate 3. Surrounded by breathtaking graphics, complex AI, and gigabytes of data, a thought wormed its way into my brain: What’s the absolute opposite of this?

My eyes landed on the dusty Game Boy sitting on my shelf. It wasn’t just about nostalgia; it was about constraints. In an age of infinite computing power, what could I create when faced with extreme limitations? Could the essence of a D&D adventure—exploration, combat, discovery—be distilled down to its purest form and squeezed onto a 32KB cartridge?

The challenge was born: Project dnd-gb. The goal: a playable, top-down RPG with a character, a dungeon, a monster, and a treasure. All from scratch. In one month.

And the “C 2025” part? That was my personal twist. I decided to use the latest C standard I could get my hands on (C23) in the year 2025, applying modern programming sensibilities to a machine from 1989. How would contemporary C features fare on a system that predates the public internet?

The Tools of the 8-Bit Trade

You can’t just fire up Visual Studio and target a Game Boy. My development environment was a motley crew of specialized, community-built tools. This isn’t a AAA studio; this is a digital garage.

• The Compiler (GBDK-2020): This is the heart of the operation. The Game Boy Development Kit is a fantastic open-source project that provides a C toolchain (using the SDCC compiler), libraries for accessing hardware, and example code. It’s the bridge between my C code and the Game Boy’s Z80-like processor.
• The Emulator (BGB): I don’t own a flash cart, so my testing happened on an emulator. BGB is more than just a way to play games; it’s a powerful debugger, offering a VRAM viewer, a disassembler, and performance profiling. It was my indispensable window into the machine’s soul.
• The Art Department (Aseprite & GB TILE DESIGNER): All graphics on the Game Boy are made of 8x8 pixel tiles. I used Aseprite to draw my character sprites and dungeon tiles within the strict 4-color palette (including “transparent”). Then, I used tools like GBTD to convert them into the C arrays the Game Boy understands.

To put the hardware challenge in perspective, consider this:

The 30-Day Gauntlet

With my tools assembled, the clock started ticking. I broke the monumental task into weekly sprints.

Week 1: Hello, Dungeon! and Basic Movement

The first week was a lesson in humility. My first goal: get a single sprite on screen and move it with the D-pad. It sounds simple, but it involves understanding VRAM, sprite attributes, and the hardware input register. After two days of staring at a blank screen, the moment my little @ symbol blinked into existence was pure magic. It felt more rewarding than any complex algorithm I’d written in my day job.

By the end of the week, my @ could move around an empty screen. It wasn’t a game, but it was a start. The core loop—read input, update state, draw—was alive.

Week 2: Building the World (and Bumping Into It)

This week was all about creating a place for my hero to explore. I designed a simple 20x18 tile dungeon map—the maximum that fits on the Game Boy screen. This meant drawing wall tiles, floor tiles, and a door in Aseprite, converting them, and writing code to load the map into the background layer.

Then came collision. How do you stop the player from walking through walls? Without a physics engine, the solution is beautifully simple: before moving the player, check the tile ID of the destination. If it’s a wall tile, just… don’t move. It’s a crude but effective system that perfectly embodies the Game Boy’s programming philosophy.

The biggest challenge is memory. You can’t just load a giant level. Every tile, every sprite, every line of code is precious real estate in your 32KB of ROM.

Week 3: The “RPG” in RPG

With a world to explore, it was time to make it dangerous. This was the most complex week, where the D&D influence truly came into play.

First, stats. I created a simple struct for the player and monsters, containing just HP and Attack Power. No Charisma checks here.

Next, combat. I implemented a simple turn-based system. When the player moves onto a monster’s tile, the game switches to a “combat mode.”

1. The player presses ‘A’ to attack.
2. A random number is generated (my stand-in for a d20 roll).
3. Damage is calculated and the monster’s HP is reduced.
4. The monster attacks back.
5. Repeat until one is defeated.

It’s a far cry from the tactical depth of a real TTRPG, but on the small screen, it felt surprisingly tense. Seeing “You defeated the Slime!” pop up in the Game Boy font was a genuine thrill.

Week 4: The Final Boss: Polish and a Playable Loop

The final week was a frantic blur of bug-fixing and feature creep. The core game was there, but it didn’t *feel* like a game. It needed polish.

I used a tool called GBT Player to add a simple chiptune dungeon theme and some blippy sound effects for attacking and taking damage. The difference was night and day. Sound is half the experience, even when it’s coming from a tiny, tinny speaker.

Finally, I added a win condition: a treasure chest at the end of the dungeon. Touch it, and a “You Win!” screen appears. Die to a monster, and you get “Game Over.” A complete, playable loop, from start to finish. It was short, simple, and probably full of bugs, but it was *mine*.

What I Learned (Besides Sleep Deprivation)

So, was the insane 30-day challenge worth it? Absolutely.

Programming for constraints is a superpower. When you only have 8KB of RAM, you stop thinking about fancy data structures and start thinking about clever bit manipulation. It forces you to write efficient, purposeful code. It’s a skill that’s incredibly valuable even in the world of abundant resources.

Modern C on old hardware is an interesting mix. While I couldn’t use the standard library (no `malloc` or `printf` here!), some C23 features were surprisingly nice. Using `nullptr` instead of `NULL` felt cleaner, and new preprocessor directives like `#elifdef` made managing different hardware versions (like Game Boy vs. Game Boy Color) a bit tidier. It was mostly a stylistic exercise, but a fun one.

The finish line is just the beginning. My 30-day game is more of a prototype than a finished product. But it works. It’s a foundation I can build on. More importantly, it proved that the idea wasn’t so insane after all.

If you’ve ever had a crazy project idea rattling around in your head, my advice is simple: just start. Give yourself a deadline, embrace the limitations, and build something. You’ll be amazed at what you can create when you trade infinite possibility for focused execution.

Now, if you’ll excuse me, I think my little @ hero has a dragon to fight in version 2.0.

You can check out the (admittedly messy) source code for this project on my GitHub! (Link to be added)