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.
Complete the last level with a single bullet.
Welp, there you go.
Complete the White Pawn Scenario.
Solve Vinny's riddle on your first attempt.
Find the developer's future game concept art.
Complete the Black Pawn Scenario.
Press E on every single bloody thing.
Screw around in the fireplace.
Stop looking at the damn picture.
A sizeable achievement.