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 all Buccanary coins.
Unlocked every trinket from Buccanary's shop.
Mastering trinket collection at Buccanary's!
Listened to the shell near the old ruins.
Collected the Golden disks.
Tried to report to Asio at the first sign of trouble.
Cleared the Boguins' Cannon challenge.
Collected Buccanary coins.
Beat Geddy 1000 times.
Learned how to cope with the heat in Toby's hot spring.
Played Otus's song on Bomboman's drums.
Threw Geddy into the clouds! How rude!