Complete the following tasks to unlock the corresponding achievement. To view your achievements and stats in Steam, select "Community", then "My profile", then "View all my games", then the game and view stats.

Achievement	How to unlock
Cleaning Up	Collect all the fireflies in 'Every Kite Soars' in a single run.
Courage	Act III completed.
Fear	Act II completed.
Firefly Collector	Collected 100 Fireflies.
Firefly Enthusiast	Collected 500 fireflies.
Firefly Lover	Collected 1000 fireflies.
Firefly Master	Collected 1500 fireflies.
First Steps	First Level Completed.
Mastering the Underground	Complete all Bonus Levels.
Ouch Free	Beat 'All Around is Petrified' without taking any damage.
Shy of the Firefly	Beat 'Deep Sleep Dive' without collecting any fireflies.
Wonder	Act I completed.