Here is the full list of all 58 Final Fantasy IV (3D Remake) achievements. It takes around 80-100 hours to unlock all of the achievements on Windows.
You earned all achievements.
You completed the entire Bestiary.
You defeated Geryon.
You defeated Proto-Babil.
You finished the game twice.
You finished the game on Hard difficulty.
You acquired all hidden summons.
You obtained all the Onion items.
You obtained Adamant Armor.
You earned 500,000 gil.
You defeated 2,000 enemies.
You raised Cecil (Paladin) to level 70.
You obtained all augments.
You traveled across the entire map.
You finished the game.
You played through all Namingway events.
You earned 200,000 gil.
You talked to everybody in the Training Classroom.
You obtained Ragnarok, Holy Lance, Murasame, and Ribbon.
You defeated the CPU.
You defeated the elemental archfiends.
You acquired all summons.
You went to the moon on The Lunar Whale.
You obtained Excalibur.
You obtained 20 augments.
You defeated Demon Wall.
You defeated 1,000 enemies.
You raised Cecil (Paladin) to level 50.
You completed 60% of the Bestiary.
You defeated Rubicante.
You defeated Dr. Lugae.
You talked to everybody in the Developers' Office.
You defeated Calcabrina.
You defeated Barbariccia.
You defeated the Magus Sisters.
You earned 50,000 gil.
You raised Cecil (Paladin) to level 30.
You defeated Dark Elf.
You defeated 500 enemies.
You completed 30% of the Bestiary.
You raised Cecil (Paladin) to level 20.
You defeated Cagnazzo.
You earned 10,000 gil.
You raised Cecil (Paladin) to level 10.
You defeated Scarmiglione.
You raised Cecil (Dark Knight) to level 25.
You were shipwrecked by Leviathan.
You raised Cecil (Dark Knight) to level 20.
You defeated Mom Bomb.
You defeated the Sahagin that attacked at Kaipo.
You completed 10% of the Bestiary.
You traveled to Damcyan Castle.
You defeated 100 enemies.
You raised Cecil (Dark Knight) to level 15.
You obtained one augment.
You acquired one summon.
You traveled to Mist.
You played a new game.