Unlock Hardened Detective mode
     Finish the game on the Private Investigator difficulty level with
any Mythos rank

Unlock Mythos Master mode
     Finish  the  game on the Hardened Detective difficulty level with
any Mythos rank

Unlock Background art renders
     Finish the game on the Private Investigator difficulty level with
any Mythos rank

Unlock Character art renders
     Finish the game on the Private Investigator difficulty level with
any Mythos rank

Unlock Concept artwork
     Finish the game on the Private Investigator difficulty level with
any Mythos rank

Unlock Craig Mullins gallery
     Finish  the  game on the Hardened Detective difficulty level with
any Mythos rank

Getting "A" rank:
     Reach 100% game completion.

You have to complete the following objectives to reach 100% completion:
Find all journal entries
- Jack's Diary: 13 entries 
- General Evidence: 18 entries 
- Mythos Tomes: 6 entries 

Find the rifle at reception door
Save Ruth
Keep enough sailors alive in boat
Finish the entire game in under 3.5 hours 
Less than 30 saves.

Safe combinations:
     Note: Jack Walters needs to find the clue before the open the safe.

Opening the safes:
1st number: start rotating the dial clockwise
2nd number: rotate the dial anti-clockwise
3rd number: rotate the dial clockwise again
4th number: rotate the dial anti-clockwise again

Variety Store safe: 
Clue is in Waite residence attic. 
The safe combination is 2 - 6 - 1 - 2. 

Church Basement safe: 
Clue is to use postcard on number tablet. 
The safe combination is 3 - 1 - 5 - 7. 

Precinct safe: 
Clue is in cell next to Brian's cell. 
The safe combination is 1 - 8 - 4 - 6. 

Masonic Hall safe: 
Clue is in second floor study. 
The safe combination is 1 - 8 - 7 - 8.