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