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