Here is the full list of all 10 Only If achievements. It takes around 2-3 hours to unlock all of the achievements on Windows.
Find the developer's future game concept art.
Complete the Black Pawn Scenario.
Welp, there you go.
Solve Vinny's riddle on your first attempt.
Complete the White Pawn Scenario.
Complete the last level with a single bullet.
A sizeable achievement.
Press E on every single bloody thing.
Screw around in the fireplace.
Stop looking at the damn picture.