Here is the full list of all 12 Owlboy achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
Collected the Golden disks.
Beat Geddy 1000 times.
Unlocked every trinket from Buccanary's shop.
Mastering trinket collection at Buccanary's!
Collected Buccanary coins.
Collected all Buccanary coins.
Listened to the shell near the old ruins.
Cleared the Boguins' Cannon challenge.
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.
Played Otus's song on Bomboman's drums.