Here is the full list of all 30 FINAL FANTASY IV achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Earned all achievements.
Completed 100% of the Bestiary entries.
Reached level 70 for all party members.
Defeated Zeromus and restored peace to the world.
Collected treasure from 100% of the chests.
Obtained all sealed equipment.
Obtained all hidden items.
Exchanged the pink tail for Adamant Armor.
Traveled to all the map locations.
Found and learned all secret summon magic.
Defeated the four elemental lords again.
Obtained Excalibur.
Learned all non-secret summon magic.
Obtained the Lunar Whale and landed on the moon.
Obtained 500,000 gil.
Defeated Rubicante, the Lord of Fire.
Defeated 1000 monsters.
Completed 50% of the Bestiary entries.
Collected treasure from 50% of the chests.
Arrived in the underworld.
Defeated Barbariccia, the Lord of Wind.
Obtained 100,000 gil.
Defeated Cagnazzo, the Lord of Water.
Defeated 500 monsters.
Climbed Mt. Ordeals and became a paladin.
Obtained 10,000 gil.
Collected treasure from 10% of the chests.
Completed 10% of the Bestiary entries.
Defeated 100 monsters.
Accidentally destroyed the village of Mist.