X-CulT: Nintendo 64 > Legend of Zelda: Majora's Mask > General Information
Debug Build
A debug build of Majora's Mask was purchased and dumped by cendamos. Not much is known about its contents yet, but the second half of the 64MB rom is apparently Ocarina Of Time debug information from a presumed prototype version of the game.

The original release thread: http://zelda64.net/forums/index.php?topic=2437.msg