FESTOON

String the festival lanterns through an old tree. Light every one with the fewest strings there are.

Every fork of the tree holds a dark paper lantern. Press A on one to start a string, then run it along the limbs with the D-pad (small arrows show which direction takes which limb): every lantern it reaches lights up in that string's colour. No lantern can hang on two strings, so a string can never run through a lantern that is already lit. Press A again to tie it off; B pulls it back one limb, and unties the last string if you change your mind. While a string is open, the frame round your lantern takes that string's colour.

Light the whole tree with as few strings as you can. The obvious plan, running the longest string you can first, misses par on most of the forty trees: the trick is where the strings meet at the forks.

Every tree has a proved par

For each of the forty trees, the fewest strings that can ever light it was worked out exactly on a computer before the cartridge was built. That is PAR on screen. Light it on par for GOLD, one over for SILVER, two over for BRONZE. After you light a tree, press B to watch the proved par plan strung from a bare tree, string by string.

Forty generated trees, in Game Boy Color

Every tree is drawn by the game's own renderer, limbs tapering from the trunk to the twigs, and no two are the same shape. Every string is its own colour. All forty trees are open from the start, and the cartridge keeps your best medal on each one in its battery save. Light the last one and the cartridge says so.

A real Game Boy Color ROM

This is a 512 KB MBC5 cartridge image with a battery save, written in C with GBDK-2020, for the Game Boy Color only: a 160x144 screen and the console's own sound chip for the music and the chimes. The free edition on this page is the first ten trees, running in your browser on the binjgb emulator, and it keeps its medals in your browser. The $4.99 download is the full cartridge: all forty trees and the ending, as a .gb file for the emulator or flash cartridge of your choice, with a manual. We have tested it in an emulator, not on real hardware.

Controls. D-pad (arrow keys): run a string along a limb (hold to keep going), or move to another lantern when no string is open. A (X or Space): start a string on a dark lantern, or tie the open one off. B (Z): pull the string back one limb, or untie the last string; after a solve, show the par plan. START (Enter): start the tree again (with lanterns lit it asks first; press it twice); on the tree list, the rules again. A, B, START or SELECT stops the par plan. SELECT (Shift): the tree list (it asks first, like START, if lanterns are lit), where SELECT turns the sound off and on. M mutes the browser page. On a phone, an on-screen pad appears.

Paid, from the same studio: WISPCATCHER ($5.99), a Game Boy pursuit puzzle: a wisp hops one fork of a generated tree every night, and you catch it in the proved fewest dawns · CRAQUELURE ($5.99), a Game Boy Color game about catching forged paintings by changing the lamp · WARDLOCK ($7.99), forty-eight generated warded locks for the Game Boy, each shipped with its shortest solution · everything else at csaf.itch.io

Made by Core Systems Asset Factory. The puzzle underneath, covering a tree with the fewest paths that share no fork, is a classical problem in graph theory; the trees, the pars and the plans are generated and computed by our own code.

AI disclosure: the code, art and text were made with generative AI assistance. The cover is key art: the game's own tree and lanterns with a glow and a banded dusk sky added that the cartridge does not draw. The screenshots and the GIF are the cartridge's own screens. The music and sound effects are the Game Boy Color's own sound channels driven by that code, not the output of a generative audio model.