In each level, the player must complete certain objectives and then exit the stage.[1] The requirements are varied, with many levels requiring the recovery and use of numerous high-tech gadgets. If Joanna is killed or fails an objective, the player must start the level again. Three distinct difficulty settings are available for each level, the choice of which will affect aspects such as the number of objectives that must be completed, enemy accuracy and damage, the effectiveness of the game's optional automatic aiming assistance, and the availability of ammunition and items such as protective shields.[1][10] If all the levels are completed on the highest difficulty, an additional setting becomes available, titled "Perfect Dark".[1] In this mode, players can customise various aspects of enemies, such as their health, their aiming accuracy and the damage they inflict.[1] In addition to the main campaign, there are four bonus missions, with three enabling the player to control other characters with unique special abilities.[11][12] Players can also unlock cheats by completing the levels within certain time limits.[13] Some cheats can alternatively be unlocked by using the Perfect Dark Game Boy Color game and Transfer Pak.[14]