All Secret Missions Locations Guide (Secrets Exposed Trophy)
There are a total of 12 Secret Missions to find in DMC5. You need to complete all twelve of them for the Secrets Exposed achievement / trophy.
None of the Secret Missions are missable. As soon as you interact with one in a mission, you can either play it there and then or play it later in the Secret Missions menu.
For the Secret Missions you need to complete a specific objective, such as maintaining an S Rank or reaching an area in a certain amount of time.