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.
Defeated Chaos and restored peace to the world.
Reached level 50 for all party members.
Obtained Excalibur.
Restored the Wind Crystal's light.
Traveled to all the map locations.
Restored the Water Crystal's light.
Gained titles of courage from Bahamut.
Collected treasure from 50% of the chests.
Completed 50% of the Bestiary entries.
Restored the Fire Crystal's light.
Restored the Earth Crystal's light.
Obtained 100,000 gil.
Obtained 50,000 gil.
Collected treasure from 10% of the chests.
Defeated 500 monsters.
Obtained 10,000 gil.
Defeated 300 monsters.
Completed 10% of the Bestiary entries.
Saved Princess Sarah by defeating Garland.
Defeated 100 monsters.
Earned all achievements.
Played the 15 Puzzle game.
Completed 100% of the Bestiary entries.
Collected treasure from 100% of the chests.