where precisely the line is drawn between mere improvements and game-changing mods.
Complete: A Complete hack has its own identity and an established premise of change applied throughout the entire game (levels, graphics, text, etc.). It should not appear as a minor variation of the original game, nor contain partially implemented ideas. For instance, a complete graphics and level hack would consist of most or all graphics and levels changed.
tl;dr If all levels are modified significantly, its a Complete hack.
Spoof: Complete Hacks that specialize in humor, usually being parodies of the original game. They also frequently contain adult content. The same rules apply to them as do Complete hacks.
Its a Complete hack with "more stuff."
Improvement: These hacks improve on some aspect of the original game, while leaving the majority of the original content intact. Game Improvement hacks must be in the spirit of an extension or enhancement to the original game. An example would be a hack that adds a new powerup to a platformer, or a new magic spell in an RPG. Improvement hacks are often ones intended to be used as a base for other hacks. While hacks that rebalance difficulty or modify game mechanics may be considered improvement hacks, those that apply simple cheats (infinite lives, invincibility, game genie or pro action relay codes) are considered out of scope for RHDN.
tl;dr If it adds a new feature in a game with no significant level design changes, its an Improvement.
Bugfix: A subcategory of Improvement for easy filtering; these are Improvement hacks that only fix bugs in the original game. This covers code, data and/or graphical fixes.
tl;dr This FIXES the original game.
Addendum: A hack that fixes bugs, improves upon, or revamps another author’s released hack. The resulting patch is intended to be a non-translation hack. Patches should contain addendum work only unless it is not possible due to the technical requirements of the patch (such as patches targeting a different ROM). Significant improvements that cause the hack to take on a new identity are exempt and may be submitted under the Complete category.
tl;dr This FIXES or IMPROVES another hack.