Take Flight – Take to the skies on an animal
To get this achievement, you need to follow the Take Those Broken Wings and Learn to Fly questline that is given to you by Rosa in the Witching Woods.
After you’ve visited Autumn, you can use the same bigify potion used on an animal in the early game on a bird. Conveniently, there is a raven outside Autumn’s house. Use it on the bird and you will get the achievement.