Finish desired World of Balance errands, shop and learn spells.
Walkthrough
The next major story sequence ends the World of Balance. Visit places and shops you still want to see, collect time-limited magicite and check the enemy encounters and treasure you care about. Some chests deliberately change contents later, so a completion target and a stronger-item target may call for different choices.
Recruit 
Mog in Narshe if you want his water dance in the original release. Take him through a water-terrain battle such as the Serpent Trench before departing. Later releases have different opportunities; the GBA Leviathan battle offers another water-terrain chance.
Equip three members for the airship assault, with healing and elemental coverage spread among them. Save in a separate slot, stock recovery items and be aware that Pixel Remaster bestiary completion has encounter-specific requirements during the air battle.
Checkpoint
Save separately before the assault. Consider early Mog recruitment and the water dance, one-time enemies, magicite, changing chests and shop stock. The Pixel Remaster bestiary and the original cartridge have different completion considerations; a single checklist cannot safely establish every version’s requirements.