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.
Defeated the emperor and restored peace to the world.
Collected treasure from 100% of the chests.
Leveled up one magic spell to skill level 16.
Traveled to all the map locations.
Leveled up one weapon type to skill level 16.
Obtained Excalibur.
Learned all passwords.
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.
Completed 50% of the Bestiary entries.
Defeated Commander Gottos and reclaimed Castle Fynn.
Obtained a ship from the pirate Leila.
Blew up the Dreadnought.
Collected treasure from 10% of the chests.
The empire destroyed numerous towns with the Dreadnought.
Completed 10% of the Bestiary entries.
The rebellion commenced against the Palamecian Empire.
Obtained 100,000 gil.
Defeated 500 monsters.
Obtained 50,000 gil.
Defeated 300 monsters.
Obtained 10,000 gil.
Defeated 100 monsters.