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