Here is the full list of all 12 Owlboy achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
Played Otus's song on Bomboman's drums.
Tried to report to Asio at the first sign of trouble.
Threw Geddy into the clouds! How rude!
Learned how to cope with the heat in Toby's hot spring.
Mastering trinket collection at Buccanary's!
Unlocked every trinket from Buccanary's shop.
Listened to the shell near the old ruins.
Beat Geddy 1000 times.
Cleared the Boguins' Cannon challenge.
Collected Buccanary coins.
Collected all Buccanary coins.
Collected the Golden disks.