Here is the full list of all 24 FINAL FANTASY achievements. It takes around 12-15 hours to unlock all of the achievements on Windows.
Collected treasure from 100% of the chests.
Reached level 50 for all party members.
Obtained Excalibur.
Played the 15 Puzzle game.
Defeated Chaos and restored peace to the world.
Restored the Wind Crystal's light.
Traveled to all the map locations.
Restored the Water Crystal's light.
Collected treasure from 50% of the chests.
Gained titles of courage from Bahamut.
Restored the Fire Crystal's light.
Completed 50% of the Bestiary entries.
Restored the Earth Crystal's light.
Obtained 100,000 gil.
Obtained 50,000 gil.
Collected treasure from 10% of the chests.
Defeated 500 monsters.
Defeated 300 monsters.
Obtained 10,000 gil.
Completed 10% of the Bestiary entries.
Defeated 100 monsters.
Saved Princess Sarah by defeating Garland.
Earned all achievements.
Completed 100% of the Bestiary entries.