The portal to Galuf's World is in the middle of the map.
Step on the portal to teleport to Galuf's World.

Deserted Island
You'll reappear on Deserted Island.
Bestiary: Pao
This monster only spawns here. Since you won't visit here again, let's get the bestiary now.
Note: it'll always drop Tent in case you want to farm it... lol.
Save your game before continuing.
Walk into the forest to trigger a scene.
You'll have to fight a mini-boss here. Whether you win or lose, the story continues. However, you'll miss the bestiary entry if you lose, so I suggest you reload the game until you win.
Scenario 1: Win the battle, open the chest, you get poisoned, they kidnap you.
Scenario 2: Lose the battle, Abductor will kidnap you.
Boss: Abductor
Guaranteed Drop: Ether
Pretty standard fight, just spam your physical or magic attacks and heal using potions if needed.
Castle Exdeath
Follow the map below to B3 to rescue everyone. Enemies start spawning on B2 and B3.
Bestiary Checklist:
Note: Spear is a missable weapon. It's pretty basic and nothing special, but it can only be obtained by stealing from Shell Bear with a success rate of about 3%. If you are a completionist and want to collect everything, you might want to get it. 3 Thieves and 1 White Mage should make the steal easier.

Boss: Gilgamesh (1st encounter)
Guaranteed Drop: Elixir
This boss has 11500 HP; however, he'll run away after losing 1500 HP.
Skills that can finish the battle in one hit are Gravity (Time Mage), Missile (Blue Mage), Zeninage (Samurai). The choice is yours. Jobs with physical attacks may take some time to defeat the boss.
Note: Missile tends to miss a lot, and Zeninage costs a lot of gil, which makes Gravity the best option in this battle.
Backtrack to 1F and exit via the south exit.
Overworld Missable Bestiary
These monsters spawn around the Castle Exdeath area, and they are missable. Make sure you collect them now: