What is moon-below?

Moon Below is a horror adventure game built to run entirely on an original Nintendo Game Boy, with no internet connection or outside server involved. What makes it unusual is that the narration text you read during the game is not pre-written. Instead, a tiny language model, a scaled down version of the kind of AI that generates text, runs directly inside the game cartridge and generates the wording word by word as you play. The story itself is fixed: you wake beneath a ruined observatory during an eclipse and must reach the Moon Gate before morning, choosing what happens along the way. The observatory has fourteen locations, ten important objects, three different routes through it, and six different endings, all determined by fixed game logic. A creature called the Warden reacts to noise rather than following a scripted path, so playing quietly or triggering loud machinery changes how it behaves. The technical trick is that the game engine tracks the true state of the world, such as where you are and what has happened, and turns that into a short sequence of tokens the tiny transformer model reads. The model then generates up to ten words, chosen only from words that make sense for the current situation, using a random seed so that the exact wording can differ between playthroughs even when the underlying events are the same. The developer is explicit that this is not simply picking from a table of pre-written sentences, and the game includes a way to inspect the model's internal state during play to prove this. The model itself is extremely small, about 15,840 parameters and a vocabulary of 232 tokens, small enough to fit inside the tight memory limits of Game Boy hardware. The project builds on an earlier related project called DMGFormer, which provides the reusable transformer engine. Building the game from source requires a specific Game Boy development toolchain called GBDK-2020. All of the project's own code, along with the trained model and its assets, is released under the MIT license.