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