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