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.
Reached level 50 for all party members.
Won 10 battles in the coliseum.
Acquired all "Bushido" commands.
Obtained all "Tools" commands.
Reunited with 10 allies.
Acquired all "Blitz" commands.
Reunited with 5 allies.
Completed 50% of the Bestiary entries.
Reunited with 1 ally.
Witnessed the Warring Triad revive and destroy the world.
Obtained 15 pieces of magicite.
Defeated 2,000 monsters.
Collected treasure from 50% of the chests.
Won an item at auction.
Obtained 500,000 gil.
Attended Emperor Gestahl's banquet and brokered peace.
Used the "Leap" command to learn 50 enemy techniques.
Defeated 1,000 monsters.
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.
Collected treasure from 10% of the chests.
Met with Banon and decided to oppose the Empire.
Obtained 10,000 gil.
Defeated 100 monsters.
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.
Completed 100% of the Bestiary entries.
Collected treasure from 100% of the chests.
Obtained all hidden items.
Traveled to all the map locations.