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