Here is the full list of all 9 The Haunting of Billy achievements.
Find your way off the level.
Don't take Bucky with you.
Have on you 250 candy at one time.
Find and equip Bucky's pan.
Wear a full costume where every piece is unique.
Wear a full costume set.
Blow an enemy clean off the level.
Look at that lil' devil!
Meet your loving and caring guardian demon.