Here's a thing I decided to work on recently, a MMC5 mapper conversion for Kirby's Adventure. The goal was to use the MMC5's increased PRG ROM capacity to make managing free space less of a hassle when editing levels (I'm willing to wager that you could probably make every room in the game be as large as possible and still not run out of space).
This patch is for the US PRG0 version of the game, but I plan to adapt it to other versions later. Note that the patch is not compatible with current releases of the editor, but the next release will include it as an optional feature just like the "expanded level header" patch it currently has.
Aside from the increased space, everything in the game should be exactly the same as in the original MMC3 version. I'd appreciate some additional eyes to make sure everything works fine. (The parallax scrolling during the Nightmare Orb battle probably needs some tweaking, but it's already kinda flickery in the original game, so there's not a whole lot I can do about that.)
Along with this, I'm planning to include some other stuff that is probably overdue, like freehand drawing, etc. in the next version of the editor.