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