Here is the full list of all 37 FINAL FANTASY VI achievements. It takes around 40-50 hours to unlock all of the achievements on Windows.
Earned all achievements.
Completed 100% of the Bestiary entries.
Defeated Kefka and restored peace to the world.
Collected treasure from 100% of the chests.
Learned 20 enemy techniques.
Obtained all magicite.
Traveled to all the map locations.
Won 10 battles in the coliseum.
Used the "Leap" command to learn 50 enemy techniques.
Reached level 50 for all party members.
Obtained all "Tools" commands.
Obtained all hidden items.
Acquired all "Blitz" commands.
Acquired all "Bushido" commands.
Defeated 2,000 monsters.
Reunited with 10 allies.
Reunited with 5 allies.
Obtained 500,000 gil.
Completed 50% of the Bestiary entries.
Reunited with 1 ally.
Witnessed the Warring Triad revive and destroy the world.
Collected treasure from 50% of the chests.
Attended Emperor Gestahl's banquet and brokered peace.
Got "Joker's Death" with the "Slot" command.
Defeated 1,000 monsters.
Obtained 15 pieces of magicite.
Won an item at auction.
Performed in the opera and obtained the airship.
Encountered Ramuh and obtained his magicite.
Obtained 100,000 gil.
Protected the frozen esper and ousted the Imperial troops.
Completed 10% of the Bestiary entries.
Met with Banon and decided to oppose the Empire.
Collected treasure from 10% of the chests.
Defeated 100 monsters.
Obtained 10,000 gil.
Encountered the frozen esper and awakened elsewhere.