Recently I played Zelda Minish Cap for the first time and after getting through the first dungeon I realized the game was just like the Oracles and needed a level editor. I've only attempted GBA hacking once before but regardless I dove right in and now it's a project that's made decent progress. Right now it only has map viewing, which I'm pretty sure is flawless but I'm not entirely sure since I haven't even beaten the game yet! Here's a screenshot.
The layout isn't official or anything but to actually get the maps displaying took a few days. The compression used is the regular GBA LZ77 for everything. Before releasing it, I plan on having the basic stuff for a hack - character editing, warp editing, map property editing (I already have this data figured out), connection editing, level editing (obviously), chest editing, and anything else I feel is necessary.
~Lin
