WWF No Mercy was notorious for a massive memory glitch that would delete all of the player's save data at any time. A fixed version was released almost a year later. The new version also had blood removed, although animations and "first blood" matches remained in the game.
The Big Show was originally intended to be featured in the game, however he was removed during development due to his contract expiring. However, using a Gameshark, it's still possible to access his face texture in Wrestler Edit mode. The name of the face texture is RROR (for ERROR).
It was originally intended for the game to have Transfer Pak functionality, allowing the player to take their created wrestler in the Game Boy Color version and place him into the Nintendo 64 version. The Game Boy version was cancelled, but the menu can still be accessed using Gameshark codes.