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