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