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