Chapter 3 missable achievement (streamlined solution) - after Wilbur tells Ivo about the ghost, and you switch to her to ask for help, go to the two-headed ogre first. ask about ghosts and choose the dialogue about his amulet, which he refuses to part with.
now head to the main entrance of the mage school and tell the troll you have a delivery for little Chantal. you will need to have taken the doll from the headmaster's office as Wilbur, and given it to Ivo. the troll will plug his ears, so you can use the green fire to access the school and he won't hear the slate give the code to the office.
once inside, "look at the desk" at the far right, then interact with it again 4 times, selecting the first 4 options to write some new laws. the one about the amulet is not available if you didn't already speak to Blout about his amulet, so you'd need to backtrack to him and return here. afterwards, you should have 4 laws in your inventory and the achievement should be unlocked.