The Pixel remaster version of Final Fantasy III has 19 chests and 3 hidden items that are permanently missable if you don’t get them in a timely manner. This Seeking Tech guide will help you find these collectibles.
You can use the following video as a reference when it comes to the locations of these missables:
Castle Hein
Castle Hein can only be visited once. Once you are brought there unwillingly, you need to talk to the guard standing on the left wall to get the hidden item.
Afterwards, cast Mini on your party to escape on the small opening on the north wall. You then need to find the 11 chests located inside this dungeon before confronting the boss.
Wrecked Ship
The Wrecked Ship is where you need to go when you visit the second world for the first time. There are two chests here.
Make sure you grab them before you complete the Cave of Tides dungeon as the ship will disappear.
Southwestern Saronia
Southwestern Saronia has two hidden items that are easily missable. As part of the story, your airship will get shot down, forcing you to drop down to Saronia.
In order to progress, you need to head over to Southwestern Saronia. In this location, head over to the house on the upper right side. After some story and a battle, Prince Alus will join you as a guest.
With him in tow, you need to talk to two separate NPCs in Southwestern Saronia so that they will give you the hidden items.
Doga’s Grotto
Doga’s Grotto is another one-time dungeon. You need to find all 6 chests here before you beat the bosses, and teleport out of the location. Otherwise, you will miss out on all the treasures in this area.