One you have acquired camera, you'll be able to do special exorcism missions. During the Night, as the Werehog, sometimes when you talk to certain townspeople they will act all depressed and purple stuff will appear. This means you can perform an exorcism on them by pressing
. You'll then need to just beat the mission by destroying all the enemies. You will have to do every exorcism for the achievement to unlock.
There is only one in every village (excluding Eggman Land), while Spagonia has two and Apotos has three.