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.
Obtained all "Tools" commands.
Obtained all hidden items.
Acquired all "Blitz" commands.
Used the "Leap" command to learn 50 enemy techniques.
Acquired all "Bushido" commands.
Reunited with 10 allies.
Won 10 battles in the coliseum.
Obtained 500,000 gil.
Reunited with 5 allies.
Completed 50% of the Bestiary entries.
Reunited with 1 ally.
Witnessed the Warring Triad revive and destroy the world.
Defeated 1,000 monsters.
Obtained 15 pieces of magicite.
Collected treasure from 50% of the chests.
Attended Emperor Gestahl's banquet and brokered peace.
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.
Earned all achievements.
Defeated Kefka and restored peace to the world.
Obtained all magicite.
Got "Joker's Death" with the "Slot" command.
Learned 20 enemy techniques.
Reached level 50 for all party members.
Completed 100% of the Bestiary entries.
Collected treasure from 100% of the chests.
Traveled to all the map locations.