Here is the full list of all 28 FINAL FANTASY II achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
Collected treasure from 10% of the chests.
The empire destroyed numerous towns with the Dreadnought.
The rebellion commenced against the Palamecian Empire.
Obtained 100,000 gil.
Leveled up one weapon type to skill level 16.
Leveled up one magic spell to skill level 16.
Defeated 500 monsters.
Obtained 50,000 gil.
Defeated 300 monsters.
Completed 10% of the Bestiary entries.
Obtained 10,000 gil.
Defeated 100 monsters.
Earned all achievements.
Blew up the Dreadnought.
Obtained a ship from the pirate Leila.
Defeated Commander Gottos and reclaimed Castle Fynn.
Became allies with Ricard the dragoon.
Hatched the last wyvern egg.
The Dark Knight ascended the emperor's throne.
Past allies joined the rebel army.
Defeated the emperor and restored peace to the world.
Obtained Excalibur.
Learned all passwords.
Completed 50% of the Bestiary entries.
Completed 100% of the Bestiary entries.
Collected treasure from 50% of the chests.
Collected treasure from 100% of the chests.
Traveled to all the map locations.