It’s been confirmed that Resident Evil: Mercenaries 3D for the Nintendo 3DS is a game that once finished, cannot be reset for complete replay.
Once you’ve played the game and unlocked all the goodies, you will be unable to erase the game’s saved data and start afresh. It sounds like Capcom is fighting back against the second hand games market. It seems that Resident Evil: Mercenaries 3D for the Nintendo 3DS only supports one save file with no replay factor.
Via Tiny Cartridge