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