Remember to give it a thumbs up and favorite if it helped you, I need that stuff for self validation :)

Use them. That's it... this section's only purpose is the first -and last- friendly reminder that you have like 20 Save Slots to use as backup.

Also, do try to prioritize the missables over anything else, this will save you headaches having to reload any of the aforementioned backups :)

Actually open it... No, really
Turns out the Bestiary in the Pixel Remasters is not only an awesome compendium, but actually it basically works as a Pokedex too. It is actually so good that there is no reason for the wiki link[finalfantasy.fandom.com] to be here anymore.

Do note I am talking about the bestiary that can be accessed from the main menu when opening the game and NOT the in-game bestiary.


Display Map
This is the one feature that makes research obsolete, long story short just chase ? marks if you are planning to complete the Bestiary.

• World Monsters: These will show up as a big ? mark, if you go to the location where the mark is you will find a missing entry.
  
• Dungeon Monsters: While a little less precise, it will still show how many entries are in the dungeon and a ? mark for those missing so you know if you have completed it or need to keep running around.

Sidenote: Yes, I figured this out right before completing the Bestiary in FFIV and did not take any screenshots of the ? marks, use your imagination.

Availability:After leaving Viking Cove while riding the Enterprise.

• Bestiary: 198 - Nepto Dragon needs to be found in the water as soon as you are in this area as it will be gone should you complete Nepto Temple without fighting it at least once.
  
  Update: user @Big Bamboss shared they missed this and the bestiary still counted it, so it seems the PR has been updated to account for this missable. Leaving it here for documentation purposes.

Availability:Shortly after your first visit to Tokkul, go west from the desert to find this location.

• Location: This entire area will become missable later.
  

Note: You get the Item from this location later in the storyafter finishing Hein Castle.

Availability:You are taken here shortly after the events in Dwarven Hollows.

• Location: This is a one time only dungeon.
  
• Bestiary: 066 - Pharaoh, 067 - Lemur, 068 - Lamia, 069 - Demon, 070 - Dullahan.
  
• Chests: Get all chests in this area before fighting the boss.
  
• Extra: Make sure to talk to the guards for the Mini spell for your hidden items.

Note: You may have realized that Dullahan is an ♥♥♥♥♥♥♥. You can find him on 3F where the chest with the Royal Sword is, I found him in the "secret" hallway of said room.

Availability:As soon as you reach the Flooded World for the first time.

• Chests: Get all chests in this location.
  

Availability: Once you get access to the Enterprise after Goldor Manor.

• Bestiary: 071 - Anet, 072 - Mermaid, 073 - Seahorse, 074 - Sea Serpent, 112 - Sea Dragon.
  

Note: It would seem that in this version of the game none of these monsters are missable any longer, as confirmed by user @SH1LT* who found these monsters on the rivers.

I leave the monsters on the guide for documentation's sake in case someone from another version stumbles upon it.

* Steam decided to censor this username, so change the 1 for a "I" in your brain :)

WARNING: If you fly too close to a Castle area you will get shot down and lose the ability to land in water to fight these monsters so make sure to sail around the map until you find them.

Availability:When Alus joins your party.

• Item: Talk to the two old NPCs to receive some equipment.
  

WARNING: This can only be donewhile Alus is in your party.

Availability:After Cave of Shadows.

• Location: This is a one time only dungeon.
  
• Bestiary: 155 - Peryton, 156 - Ogre, 157 - Cyclops, 158 - Nemesis, 159 - Humbaba.
  
• Chests: Get all the chests in this location before leaving.

Availability: Before level 50.

• Thought I'd mention just in case, in FF3 the Max HP is the only stat you can "control" that is not linked to the job you are using at the moment, because of this it is theoretically possible to miss a max of 9999/9999 HP for those that care enough to grind the levels despite them not being needed to beat the game.
  
  To prevent this from happening get all characters on a job with high Vitality around level 45 and keep them on it until a century later they are all level 99, they should've hopefully maxed the HP. Even if you are like me and had a dedicated caster in your party for most of the game, they should reach max around 95.
  

• Saronia Catacombs: Dive and head to the location shown on the map below.
  
  
• Sunken Cave: Dive and head to the location shown on the map below.
  
  
• Doga's Village: Dive to the right of the location seen on the map, then go through the path on the left and hover back to the surface.
  

• Lake Dohr: Ascend into the lake area seen on the screenshot, disembark and head for the large shadow on the water.
  
  
• Bahamut's Lair: Ascend into the cave entrance seen on the screenshot.
  
  
• Falgabard: Ascend into the large path South West of Saronia, then once more into the area seen on the screenshot.
  
  
• Falgabard Cave: Find the entrance inside Falgabard's area.
  

• Use this link[finalfantasy.fandom.com] to locate and visit all 13 forests spread accross the world.
  

Hope this guide helped, now go play FFIV.