The Legend of Zelda: Ocarina of Time/Master Quest is a special re-release of the Nintendo 64 classic for the Nintendo GameCube that coincided with the release of Wind Waker.
Although the specifics of distribution differed across territories, acquiring Master Quest typically involved a pre-order of the GameCube sequel. The disc itself is split into two games: Ocarina of Time and Master Quest. Both are essentially N64 roms that use a proprietary Nintendo 64 emulator, although the latter game contains new content, largely in the form of remixed dungeons. The release of Master Quest was notable at the time, as it was believed to finally allow people to play the scrapped expansion pack to the original Nintendo 64 game, although it turned out to be anticlimactic in the end when virtually none of the more substantial new content believed to have been created actually made it into the disc.
The original Ocarina of Time portion remains completely intact, save for minor quirks that appear as a result of emulation. Likewise, Master Quest's gameplay is largely the same; its main claim to fame is in the new layouts and puzzles for the dungeons, as well as an overall higher difficulty level. A small amount of content deleted in the original game can also be found in the scenery, although its overall impact on the actual gameplay is minimal.
The origins of the Master Quest portion of the compilation lie in the development of Ocarina of Time, a game that Nintendo originally planned to add more content to in the future via an expansion pack for the failed Nintendo 64 add-on, the 64DD. Often referred to as "Ura Zelda," and occasionally confused with Majora's Mask, the expansion pack was said to be in development on numerous occasions before Nintendo quietly canceled its release, despite it being nearly finished. Little content was released to the public during Ura Zelda's creation, save for scant screenshots that are still sometimes believed to simply be deleted content from the original game. Despite the expansion's cancellation, the coding within Ocarina of Time still has mechanisms that allow the game to connect to the 64DD, although it is inaccessible via normal methods.
Public demand is what ultimately compelled Nintendo to release Master Quest for the GameCube. The release, however, proved to be controversial within the series' fan community, as it has never been determined whether that version of Master Quest was the one that was originally developed by Nintendo. Indeed, inspections of the Master Quest rom have indicated that what is on the disc is little more than a seemingly patched rom, since the game's size is the same as the original version.
Several years after Master Quest's original release, hackers going through the files on the GameCube disc were able to find a rom of Ocarina of Time which had numerous debug features turned on. Although the debug rom could only be played via emulator after it was extracted from the Master Quest disc, its discovery proved to be significant on a number of levels. Not only did the debug features allow for unprecedented control of various aspects of the game and its engine, it also included a level select that enabled players to navigate environments originally believed to have been deleted years before Ocarina of Time's 1998 release. The most significant of all was a room whose screenshots had been given to the press very early in the game's development, believed to be part of a recreation of the very first dungeon in The Legend of Zelda.