Super Spy Trophy guide
Complete a mission without being seen by a single enemy.
Trophy Type - Silver

This is one of the hardest trophies in the game. It is recommended that you work on this as soon as you can purchase the Diplomatic Pistol, and play an early story mission on Normal difficulty which allows quitting and restarting as needed until you are successful. Attempting this in later missions, or higher difficulty levels, will make things unnecessarily challenging. You need to complete the mission without being seen, so ensure that you use stealth or silenced headshots for every takedown, and skip as many enemies as possible. If you are seen for any reason, quit to the main screen and try again. If an enemy is alerted (with a ? above their head) that's OK, just don't let them see you and take them out as quickly as possible so that they don't call an alert.

Due to the dynamic nature of the levels, it isn't possible to recommend a particular level, other than to recommend that you do this as early as possible in the game on Normal difficulty.