Here is the full list of all 35 Finding the Soul Orb achievements.
Begin chapter one.
Equip the crossbow.
Shoot the gargoyle of chapter one.
Begin chapter two.
Kill the first werewolf.
Shoot the gargoyle of chapter two.
Begin chapter three.
Begin chapter four.
Equip the better crossbow.
Shoot the gargoyle of chapter four.
Begin chapter five.
Shoot the gargoyle of chapter five.
Begin chapter six.
Shoot the gargoyle of chapter six.
Begin chapter seven.
Begin chapter eight.
Shoot the gargoyle of chapter eight.
Begin chapter nine.
Shoot the gargoyle of chapter nine.
Begin chapter ten.
Shoot the gargoyle of chapter ten.
Begin chapter eleven.
Begin chapter twelve.
Shoot the gargoyle of chapter twelve.
Finish the game.
Collect the first demon at chapter 1.
Collect the second demon at chapter 2.
Collect the third demon at chapter 2.
Collect the fourth demon at chapter 4.
Collect the fifth demon at chapter 4.
Collect the sixth demon at chapter 8.
Collect the seventh demon at chapter 8.
Collect the eighth demon at chapter 9.
Collect the ninth demon at chapter 10.
Collect the tenth demon at chapter 10.