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