Here is the full list of all 12 Scary Girl achievements.
Start a Co-op game.
Purchase all the shop items.
Make the tough choice when confronted by Dr. Maybee.
Achieve a perfect status on every level.
Triumph over the dangers deep beneath the sea.
Prove your worth to Chihoohoo in a rumble with his guards.
Force your way through Warmachine to get into Bad City.
Survive Momma Yeti's cave-in.
Collect a full heart container.
Purchase a store item.
Catch an Umbrella Seed to the Old Man Mountains.
Complete a Dojo training session.