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.
Traveled to all the map locations.
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.
Reached level 50 for all party members.
Acquired all "Blitz" commands.
Won 10 battles in the coliseum.
Obtained all magicite.
Obtained all "Tools" commands.
Acquired all "Bushido" commands.
Completed 50% of the Bestiary entries.
Obtained all hidden items.
Reunited with 10 allies.
Reunited with 5 allies.
Obtained 15 pieces of magicite.
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.
Obtained 500,000 gil.
Won an item at auction.
Used the "Leap" command to learn 50 enemy techniques.
Performed in the opera and obtained the airship.
Defeated 2,000 monsters.
Defeated 1,000 monsters.
Obtained 100,000 gil.
Encountered Ramuh and obtained his magicite.
Protected the frozen esper and ousted the Imperial troops.
Completed 10% of the Bestiary entries.
Defeated 100 monsters.
Obtained 10,000 gil.
Met with Banon and decided to oppose the Empire.
Collected treasure from 10% of the chests.
Encountered the frozen esper and awakened elsewhere.