Final Fantasy IV - Spoiler-Free Guide

 

• This guide is for the Steam edition.
• You'll need to do a minimum of two playthroughs to get all achievements, and you can only do a maximum of three playthroughs - i.e., 2 new game pluses - on one file. 
• You'll need to complete the game on hard mode for an achievement.  I chose to do this on the second playthrough.
• Save your apple and soma items for your final run.  The items will carry over if unused, but the stat increases will not.
• You can open the map by pressing the right shoulder button.  Since this map shows treasure chests, I'm not going to list them.  I'm going to assume you're completing every map as you go and opening every visible chest without prompting.
• The augment system requires giving some characters augments in order to receive augments later.  I'm listing down how many augments to assign in each run to ensure you'll receive them all over two runs.  Any augments given to your non-permanent characters will be lost, so it's best to choose those which are not useful to your final team and/or which you receive multiple copies of.  I've made some recommendations to this end, supported by Jessamy's guide.  
• Once your characters reach level 70, their stats will increase based only on what augments are equipped in their command slots.  This does not include the auto-attack slot.  
• Jessamy's guide, linked above, will let you maximise stats on only two playthroughs.  However, after following it, I found it impossible to beat Proto-Babil, the bonus boss, with the recommended abilities, even at level 100 with maxed stats.  Comments on bonus boss and how I would change my augments in future playthroughs below.  I've hidden these comments because you may not be here for this level of commentary and because I reveal specific end-game party members.
• [With Limit-Break on Rydia, I couldn't do enough damage to drop his hp from 120,000 to 0 before he wiped out my party.  He begins doing very damaging attacks in this range, so rapid damage is essential.  Note that, in the Steam edition, you can only obtain one Limit-Break Augment.  You will not receive a second after your second playthrough.
• I did some experimenting with cheat engine and found that I needed to have limit-break on Kain instead of Rydia.  This allowed Kain's jump attack to do 24k-32k damage with Darkness, and Kain would not die before the attack went off.  
• I did not suffer from not having Omnicasting on Rydia, since the toughest enemies are solo.  It seems like Piercing Magic would be useful for Rosa, but I never missed it.  
• I suspect it would have been helpful to have 'Hide' on one of the same people who had Phoenix.  Probably Edge, since he can Throw while hidden.
• I'd rather have had Salve on Edge than Kain.  It was extremely useful for quickly replenishing MP and HP after Phoenix (via elixirs) and for reviving multiple characters when Rosa was KOd (via Phoenix Down).
• In short, if I were to play through the whole game again, I would give Limit-Break to Kain and Inferno and Omnicasting to Rydia.  I'd need to do some sums to see which stats they'd end up with, but I think that will still keep both close to maximum.  I'd put my second Reach on Kain for speed, and put Salve on Edge instead.]
• I've hidden the names of who to assign augments to with white text.  Highlight to read.  I've done this because sometimes knowing who's in your party is a spoiler.  Cecil never leaves, which is why I haven't bothered to hide his name.  Of course, by the time you're ready to read it, you'll know who's in your party.
• Your party changes frequently.  The name of the person who leaves will be written in white text, so highlight if you want to know whose equipment to remove.
• If I have no comments to make on an area - i.e., there's nothing to get there but what's marked on the map - it will be skipped entirely.  

First Playthrough

Baron Castle

All -ingways look like this.

• Achievement: Customer Appreciation (automatic).
• You cannot reach the 6 chests in the basement yet.
• Speak to Namingway on your way to bed.  You can't miss him

Baron Town

• Don't buy any tents until further notice.
• Potion in a bush near the entrance, and another in a bush in the middle of town.
• Potion in a barrel in the inn.
• 3 chests upstairs in the inn, not marked on the map.  Gnomish bread, tent, and eye drops.
• The Devil's Road is in a building in the middle of the town.  Go down the stairs and speak to the five people there.  Achievement: Training Complete!.
• At the north of town, walk into the water and follow it down to the pool in the south.  There's a tent and a bronze hourglass hidden in there.
• Eyedrops behind a bush on the eastern edge of town.
• Head out of the town walls to the northeast.  Loop around north and west, to find a gold needle in some flowers, a phoenix down in a big bush, and another phoenix down in a little bush.

Mist

• Your party will change after entering the town: [Kain leaves].
• Achievement: Mission Accomplished?.

Kaipo

• Don't kill the General last.
• Speak to Mappingway in a house to the east.
• Achievement: Apprentice Summoner (automatic).
• Achievement: Augment Novice (automatic).

Damcyan

• Cecil reached level 15 and killed 100 enemies on the way.  Achievement: A Bloodstained Road and Achievement: Bronze Hunter.
• Achievement: Assault (automatic).
• From the entrance, go round to the right to find the dungeon and three chests.  There are stairs down to another 6 chests in the lower-left corner.
• Your party will change here: [Tellah leaves].

Kaipo

• In reaching this point, I'd also completed 10% of the bestiary.  Achievement: Seeker.
• Achievement: Bravery (automatic).
• After the automatic rest and battle, check north of the inn for the Item Lore augment.

Mt. Hobbs

• Achievement: Big Bang (automatic).
• Cecil reached level 20 and earned 10,000 gil on the way.  Achievement: Heaps of Corpses, Achievement: Pockets Full.  The achievement says 'earned' but it's the amount you have on hand, not the total amount you've gained.

Fabul

• Your party will change when you speak to the King: [Rosa and Rydia will leave].
• The boss battle is unwinnable.
• Speak to Livingway in the inn.
• Zeus' Wrath hidden in the candlestick in the room with three chests.
• Bacchus' Wine in a flowerpot in the room with the dancing monk.
• Hermes sandals in a pot on the left side of the throne room.
• Your party will change at the dock: [everyone but Cecil will leave].

Mysidia

• Achievement: Alone Again (automatic).
• Sell all but one tent.
• Assign two augments, possibly Item Lore and Auto-Potion, as follows: [Palom; Porom].  I rarely use items or potions to heal in battle, so neither augment represented a great loss.

Mt Ordeal

• First head to the Chocobo Forest south of the mountain.  Recordingway will take all your tents in exchange for 300g.  You can buy as many tents as you want from now, nothing will happen to them.
• Achievement: Defeated Scarmiglione (automatic).  
• Before interacting with the marker at the top of the mountain, level Cecil to 25.  Achievement: Deep into Darkness.
• Go back to the previous map to find an augment, Curse.  
• Assign one augment, possibly Curse, as follows: [Palom].  I did not find Curse useful at any point.  Many of the most powerful bosses aren't affected, and those which are don't require it.

Baron

• By this point, I had defeated 500 enemies and levelled Cecil sufficiently for an achievement.  Achievement: Silver Hunter.  Achievement: Moves toward the Light.
• Speak to Campingway in the weapon/armour shop.  You can access the two chests in here via a secret passage in the lower right.  They contain 2000 gil and a Zeus' Wrath.
• After the boss battle in the throne room, your party will change: [Palom and Porom will leave].
• Achievement: Defeated Cagnazzo (automatic).
• During this section, Cecil levelled sufficiently for another achievement.  Achievement: Walks with the Light.
• After the battle, you can find the Tsunami augment on the second level of the waterway.  Give it to Cecil.
• You can now access the 6 chests in the basement on the right-hand side of the castle.
• From the map with 6 chests, you can reach the eastern tower.  There are more chests here.  On the first basement level, you can find an elixir hidden in a candlestick.
• There's an optional cutscene on the second basement level.

World Map

• Mysidia: Speak to the Elder to receive several augments.  Assign two augments, possibly Twincast and Bluff as follows: [Tellah].  Bluff sounds like it would be useful but, in my experience, it makes very little difference to the damage you can do.  As far as I can tell, Bluff doesn't stack with itself (Focus does) and it can't seem to raise your intelligence stat above 99.  Once your intelligence is over 50, I think you'll do more damage using magic twice rather than spending one turn bluffing.  Twincast can be a very powerful attack, but it also uses up two characters turns and there are often better options.
• Mist: golden hairpin and clothing, and then a polymorph rod and a ruby ring in the first house to the north, via a secret tunnel.  Bomb fragment in a bush on the eastern edge of town.
• Agart: Island in the south.  If you wait until later, one item will be blocked.
• If you go around the central hill to the west, there's a potion and a phoenix down in a bush.
• If you get onto the big earth barrow and follow it around, there's a hi-potion in a small bush at the end.  
• There's a cottage in a large bush near the pond.  
• There's a phoenix down inside the empty house in the centre of town.  This item will be blocked later.  There's also an antarctic wind in front of this house, and a Gaia drum left of its doorway.

Troia

• Northwest continent.
• Tent in a big bush outside the armour shop.
• There are two hi-potions on the bit behind the weapon and armour shops.
• Phoenix down in the river, to the northeast.
• On the bit across the river to the northwest, there's a dry ether in a fronded plant, 1000 gil in a flower patch, ether in a rock, and a decoy in the brown patch of earth.
• Speak to Jammingway behind the inn.

Troia Castle

• Bacchus' Wine in a pot in the central area of the basement.  
• Speak to the injured man to receive Whisperweed.

Chocobo Village

• There are gysahl greens on the western edge, in the bushes in the east, and in the grass in the centre.
• In reaching this point, I'd completed 30% of the bestiary.  Achievement: Catching On.

Troia Castle

• Achievement: Saved by Music (automatic) before returning.
• Visit the injured man in the infirmary to receive the Bardsong augment.  
• Assign one augment, possibly Bardsong, as follows: [Yang].  I found Bardsong was the most useful of Edward's abilities, but that really isn't saying much.

Tower of Zot

• You cannot return here.
• Cecil reached level 30 here.  Achievement: The Gatherer of Light.
• Achievement: Delta Attack Defiance (automatic).
• Your party is about to change: [Tellah will leave].
• Pick up three augments after the party change.  
• Assign two augments, possibly Recall and Last Stand as follows: [Cid;  ang].  Last Stand is one of those that sounds useful but, I found my party members didn't spend a lot of time in critical health.  They were either safe or dead.
• Achievement: Defeated Barbariccia (automatic).
• Go back to the room in Lodestone cave where you fought the Dark Elf to find the Whirlwind augment.

World Map

• Mythril: one island in a chain on the eastern edge of the world map.  You can buy new weapons and armour here.  
• There's a Mythril knife to the right of the armour shop entrance and a Mythril staff in the northeast corner of the village.  
• There's 5000 gil in a big bush between the weapon shop and the item shop.
• There's a maiden's kiss in the eastern well and a diet ration in some flowers on the western edge, in front of the inn.
• Selling off my excess equipment here got me 50,000 gil.  Achievement: Fat Purse.
• Eblan Castle: Southwest continent.  There are no random battles, but some chests have forced encounters that you might struggle with if you come here any earlier.  You can reach all the chests.  Many are reachable via secret tunnels, some are via hidden staircases or by jumping down gaps.
• There's a Ninja Sutra hidden behind the throne.
• In the eastern tower, there are two chests.  The one on the right triggers a battle.
• In the second room in the eastern tower, there's Bacchus' wine hidden in a pot.
• In the west tower, there's a ninja sutra hiding in a flower pot in the room with two chests.  
• There are Hermes Sandals in a pot in the room above that, which contains four chests.  The rightmost chest can be reached via a secret tunnel, but also triggers a battle.  Jump in the hole near this chest to reach the one below, then jump in that hole to reach 3 chests in the basement.  Again, the rightmost one triggers a battle.  There's another Ninja Sutra hidden in a candlestick down here.
• Agart: Speak to Cheatingway in the empty house.  He wants a rainbow pudding, which can be dropped by flan enemies at a rate of 0.4%.  If you haven't received one by chance, you can farm for it later, as discussed below.  Theoretically, you could farm for it now as it is dropped by any flan.  I'm not going to because I suspect the attempt would make my brain dribble out through my ears.

Dwarven Castle

• Your party is about to change: [Cid will leave].
• In the boss battle, make sure you kill at least one Calca and one Brina.  Then leave the calcas alive and wait until the enemy uses combine before defeating it.  
• Achievement: Defeated Calcabrina (automatic).
• 5000 gil hidden near the inn counter.
• Bacchus' wine in a pot in the western tower, and another in the eastern tower.  Both are on the middle floors.
• Two sets of Gysahl Greens in the room with the Chocobo nest.
• Bomb fragment in the room with the waters of life.  It's in the middle of the floor just south of the centre, completely invisible.
• There's a pub between the weapon and item shops.  If you go through the secret passage to the right, you'll reach a staircase leading to a secret area.  Some auto-battles will trigger here, but none count towards the bestiary and you will not receive a game over if you lose.
• After speaking to everyone in the secret area, the Reach augment will appear downstairs.  Don't miss the door in the northwest on the main floor.  Achievement: Developer's Pal. 
• Lustful Lali-Ho in a bookcase in the secret area. 

Tower of Babel

• You will return here later, but not to the same areas.
• There are two ways for the boss battle to go, listed below. Each way gives you a different bestiary entry, so remember to get a different one on your second playthrough.
• Defeat the doctor.
• Defeat Barnabas.  Then stop attacking and wait for the Barnabas-Z form.  Make sure you defeat Barnabas-Z rather than letting him self-destruct.
• Achievement: Defeated Dr Lugae (automatic).
• In reaching this point, I'd killed 1000 enemies.  Achievement: Gold Hunter.
• Your party changes after you use the Lugae key: [Yang will leave].

Eblan Cave

• There is a Potion hidden in the fireplace in the infirmary.
• In reaching this point, Cecil levelled sufficiently for an achievement.  Achievement: Illuminator.
• You can access every chest.  The place is riddled with secret passages, all on the same floor as the chest you're trying to access.

Tower of Babil

• This is your final visit.
• Achievement: Defeated Rubicante (automatic).
• I reached 200,000 gil here.  Achievement: Bursting Treasure Chest.

Dwarven Castle

• Two augments in the infirmary.

Kokkol's Forge

• In the southeast.
• There is a Remedy in the boxes downstairs.
• Soma Drop in the bookcase upstairs.

Tomra

• In the south.
• Phoenix Down in a barrel in the northeast.
• Bomb core behind the item shop.
• Antarctic wind and Bestiary in the room with the chests.

Sylph Cavern

• I completed 60% of the bestiary by reaching this point.  Achievement: Aficionado.
• There's a hole in the southeast corner of B2.  Fall into it to find a secret area.
• There's a house deep within the cave.  Speak to the injured man inside.

The Passage of the Eidolons and the Feymarch

• The first area of the Feymarch village has an invisible teleport spot on the southernmost level. 
• Make sure you talk to the Eidolon in the house with the save point to begin a search quest.
• You'll need to battle Asura and Leviathan to obtain them as summons.

Sealed Cave

• Achievement: Defeated Demon Wall (automatic).
• As you walk towards the exit of the dungeon, your party will change [Kain will leave].

World Map

• You can return to the surface via a volcano in the northeast.
• Return to Mist to find the MP+50% augment.  Achievement: Augment Practitioner.
• In Troia, you can pay 100,000 gil for a member's writ to access the secret back room.  In there, there's a secret tunnel that leads to the Gil Farmer augment. 
• In the cave near Mythril, you can trade your Rat Tail for Adamantite.
• Speak to Yang's wife in Fabul.
• Steal the Darkness augment from Odin in the basement of Castle Baron.  You'll also obtain him as a summon when you win.
• Give the adamantite to Kokkol at Kokkol's forge
• Speak to the injured man in the house in Sylph's cave to obtain a summon and three augments.  
• Speak to Yang's wife again.
• You can find the Inferno augment in the Cave of Eblan.
• You can find 6 of the eidolons you're searching for at this point.  Return to the quest-giver for location hints.

The Moon

• Achievement: Promised Ship of Light (automatic). 
• Assign two augments, possibly Analyse and Upgrade as follows: [Fusoya].  Analyse was useful, but future playthroughs remember the strengths and weaknesses of enemies, and omnicasting Libra has the same effect.
• You can find the Level Lust augment in a cave in the southwest.
• You can obtain Bahamut by defeating him in a cave in the east.  Achievement: Master Summoner.

Giant of Babil

• You will not return here.
• By this point, Cecil had levelled sufficiently for an achievement.  Achievement: Paladin of Light Incarnate.
• Your party will change after the final battle here: [Fusoya will leave].
• Achievement: Defeated CPU (automatic).

World Map

• A soldier on the upper ramparts of Castle Baron will give you the HP+50% augment.
• Return to Kokkol's forge for a sword.  Achievement: Form Reborn.
• You can complete the Eidolon quest now.  You'll receive the Piercing Magic augment in exchange.  

Lunar Subterrane

• You'll find the Omnicasting, Bless, and Phoenix augments on the way.  
• In reaching this point, I'd defeated 2000 enemies.  Achievement: Platinum Hunter.
• There's a Murasame on B4 and a Masamune on B8.
• The Holy Lance is in a room off B7.
• The Ragnarok is in a room off B5.
• Having found the above weapons and the two ribbons in chests - all of which trigger battles - you will receive an achievement.  Achievement: Unsealed.
• In reaching this point, I gathered 500,000 gil.  Achievement: Time for a Vault.
• B11 is the last map in the game.  If you have completed all maps 100%, the final map you complete will give you the Treasure Hunter augment.  It appears in your inventory automatically, with a pop-up notifying you that you have it.   Achievement: The Perpetual Wayfarer. 
• I did not get the augment on this map, so I used this list to go back and check which I might have missed.  In my case, it was Underground Waterway North, B2.  I'd missed the secret passage in the southwest corner which lead to the area in the northeast. 
• Do not go past floor B11 until you want to finish the game.  
• If you do want to finish the game, make sure you steal a Dark Matter from the final boss.

End Game

• At this point, all that is left to do is complete your bestiary and grind for specific items and equipment which will be carried over to a new game plus.
• Check your bestiary with the Fat Chocobo and make a note of what you need to find.   
• I used Hawaiian Feeling's bestiary lists; 1 and 2. 
• You can go get some of them now, or you can aim to collect them all on a new game plus.  199 and 200 can only be obtained in a New Game Plus, and you'll be missing either 175 or 177 depending on how an earlier battle went.  
• Other than that, I found I needed to use Sirens outside of Kaipo and on B1 of the Ancient Waterway under Baron to get entries 11 and 45.  195 to 198 will be received automatically.
• Once I completed the bestiary, the achievement didn't unlock.  At that point, I learned that it's possible for an entry to appear in the bestiary despite you not actually defeating it.  If that happens, the slay number will be "???" and it will not count for completion.  If this happens, a common culprit is the Mystery Egg.  In my case, it was Calca, which is a boss.  I needed a third playthrough to defeat one.  Make sure you check for this issue as well so you can complete your bestiary on your second playthrough.
• If you have accidentally missed a map in the Tower of Zot, Tower of Babil, or Giant of Babil, you will not be able to access it until a new game plus.  This will mean you won't have the Treasure Hunter augment, which doubles your chances of receiving items after battle.  I don't recommend grinding for items without it.  In that case, I would suggest just finishing the game and grinding in your second playthrough.
• Speaking of grinding, I wrote a whole post on this.

Completing the -ingway Quest

• You'll need a Rainbow Pudding.  They're dropped at a rate of 1% - or 2% with Treasure Hunter - by flans.  If you aren't lucky enough to win one by chance, you'll need to farm for it.  I suggest farming Flan Princesses because they also drop Pink Tails (discussed below).
• You'll need Stardusts and Sirens.  You can do this without the Stardusts, they just speed up the process a lot.  I suggest moving them to the top of your inventory (hold the 'a' button and it will let you move an item in the list manually) just to making using Sirens and checking on your Stardust supply easier.
• You can buy Stardust at Tomra, the underground village.
• You can buy Sirens in the only town on the moon.  It's in the cave in the southwest.
• Get yourself to B5 of the Lunar Subterrane and enter the cave in the southeast.
• Equip Cecil with 'item-stardust' as his first command and his auto-command.  Give him Draw attacks, Treasure Hunter, and Counter.  Alternatively, if you need to build up your Covers for ????'s Love, give him Cover instead of Draw Attacks.
• Equip Cecil with the Crystal Mail, which prevents Berserk.  
• Put him in the back row, to reduce damage.   
• Use Siren to start a battle.  You'll face Flan Princesses.  They'll berserk everyone, but Cecil will be protected and will counter by throwing Stardusts at them.  They'll die after two or three.  Remember to heal Cecil every so often.  If you get through your entire stack of Stardusts without winning either a Rainbow Pudding or a Pink Tail, reload your game and try again.  
• Once you have a Rainbow Pudding, give it to Cheatingway in Agart.
• Speak to Puddingway in the pub in the Dwarven Castle twice to receive the Eye Gouge augment.
• Speaking to Mopingway in the Feymarch.
• Speak to Lovingway in Mysidia to receive the ????'s Love ability.  
• Speak to Weddingway in the town on the Moon where you buy Sirens.
• There are multiple places to find the last -ingway.  They're all listed in this guide.  I found him on Mt Hobbs.  
• When you do find him, he'll give you the Safe Travel augment.  Give it to Cecil.
• Achievement: Rabbit Chaser.
• Progress in this quest is retained in a New Game Plus, so if you don't grind for a Rainbow Pudding now, Cheatingway will be waiting for it in Agart in your next playthrough.

Tails

• The Tail collector in the cave near Mythril will swap any tails you find for equipment.  This equipment will be kept in a new game plus.
• The stats of Onion equipment increase with your average party level, so when you start a new game with them in your inventory, they won't look impressive immediately.
• I only got one of each thing.  You can farm for more.
• At end-game, the most useful equipment was Onion Swords and Adamant Armour.  The gloves and helms didn't really compare to other end-game equipment.  The shields were good but not essential.
• Pink Tails can be exchanged for Adamant Armor.  
• There's a 0.4% base chance you'll win it from a Flan Princess, which becomes 0.8% with Treasure Hunter.  Farm as described for the -ingway quest.
• Achievement: To the End of Misery.
• Black Tails can be traded for Onion Armor.
• Use a Siren to call Armored Fiends on floors B2 and B3 of the Lair of the Father.
•  The stats for the Adamant and Onion armours are in this FAQ.  I'd say Adamant is more useful. 
• Red Tails can be traded for Onion Swords.
• Cecil and Kain can use these.
• Use a Siren to call Red Dragons on B8-B10 of the Lunar Subterrane.
• Green Tails can be traded for Onion Helms.
• Your final five characters can use these.  
• You win Green Tails from Green Dragons.  Use a Siren just outside the entrance to the sealed cave.
• In addition, they drop Sirens at a rate of 24% and Silver Apples at a rate of 14% (with Treasure Hunter).  
• Yellow Tails can be traded for Onion Gloves.
• Your final five characters can use these.  In practice, I only farmed for one.
• Yellow Tails are dropped by Yellow Dragons.  Use a Siren just outside the entrance to the passage of the Eidolons.
• Their drops are exactly the same as Green Dragons, apart from the tails.
• Blue Tails can be traded for Onion Shields.
• Cecil and Kain can use these.  Onion Shields prevent all status effects except berserk.
• You win Blue Tails from Blue Dragons.  Use a Siren on B3 or B2 of the Passage of the Eidolons.
• They also drop Gold Hairpins at a rate of 24%.  Gold Hairpins sell for 10,000 gil each, plus you get 1962 gil per battle with Gil Hunter equipped.  Basically, don't worry about resetting.  You'll make a profit even after buying another stack of Sirens.
• Achievement: Onion Swordsman.

Hidden Summons

• There are four hidden summons that Rydia can learn.  You'll need to receive a rare drop, which has the same name as the summon, from a specific type of monster, then use the resulting item on Rydia.  Both the items and/or the abilities will be retained in a New Game Plus.
• Cockatrice
• Dropped by Helldivers, Cockatrices, or Fledging Rukhs.
• Use a Siren outside Baron.  You'll encounter 1 of 4 possible battles.  4 Helldivers; 3 Floating Eyes; 1 Sword Rat + 2 Floating Eyes; 4 Goblins.  There's an equal chance of any battle appearing, so 25% (1/4).
• The RNG chooses one enemy to drop an item per battle.  Since the battle we're interested in is all Helldivers, this is 100% (1).
• Helldivers have a 0.04% chance to drop a Cockatrice item, which is 0.08% with Treasure Hunter active (2/256).
• So, the chance of winning the Cockatrice item per Siren is; 1/4 * 1 * 2/256 = 0.2%.
• Note that you have the same odds of receiving the Goblin item while farming here, which is why I suggest doing this one first.  How annoying would it be to spend hours farming for Goblin, only to receive a second one as soon as you start farming Cockatrice?
• In practice, I got this on Siren 154.  
• Goblin
• Dropped by Goblins, Lil Murders, and Mopingway.
• Use a Siren inside the Mist Cave.  You will always face four Goblins.  
• In practice, I got it on the 142nd Siren.
• Mindflayer
• Dropped by Mindflayers.
• Use a Siren in the passage between B3 and B4 in Lodestone Cavern.  Every battle will be two Mindflayers.
• In practice, I won the Mindflyer item on the 12th Siren.
• Bomb
• You can win the Bomb item from Balloons or Dark Grenades.
• I fought them in Lunar Cave East.  Don't use a Siren, you'll just face an abyss worm every time.  I didn't fight many battles in here - I won the Bomb on the 10th - but it seems that there are four possible battles, with the following chances of encountering each: Eukaryote + 2 Dark Grenades (25%); 2 Balloons and 2 Dark Grenades (25%); Prokaryote + 2 Eukaryotes (37.5%); Abyss Worm (12.5%).  If those statistics are accurate, then you have an average 41.67% chance that the RNG will choose the right enemy to choose an item from per battle.  Since the odds of choosing the right item are 0.08% with Treasure Hunter, this becomes a 0.33% chance per battle.  
• Achievement: Expert Summoner.

Lunar Subterrane

• When you're ready to finish the game, return to the Lunar Subterrane and enter floor B12.
• Steal a Dark Matter in the final battle.  You'll need this in your second playthrough.
• Achievement: To Mother Earth (Automatic).
• You'll receive the Limit Break augment.

Second & Third Playthroughs

• If your first playthrough was on Easy difficulty, make sure you select Hard for your second.
• Watch your levels over 70.  You can influence stat gains with Augments from this point, and you'll need to take care if you want the highest stats possible.  See notes above.

Baron Town

• You cannot wear your Onion or Adamant equipment yet, but remember to equip your abilities.
• Potions: bush near the entrance of town, bush in the middle of town, barrel in the inn.
• 3 chests upstairs in the inn, not marked on the map.  
• A tent and a bronze hourglass are hidden in the river.
• Eyedrops behind a bush on the eastern edge of town.
• Head out of the town walls to the northeast.  Loop around north and west.  Gold needle in some flowers, Phoenix Downs in a big bush and a little bush.

Mist

• Unequip [Kain] before entering.

Damcyan

• From the entrance, go right to reach the dungeon.  It has nine treasure chests.
• Your party will change here: [Tellah leaves]. 
• In your second playthrough, assign two augments, possibly auto-potion and eye-gouge as follows: [Edward].  Ignore this in your third playthrough.

Kaipo

• Don't forget to grab the Item Lore augment behind the inn.  

Fabul

• Your party will change here: [Rosa and Rydia will leave].
• Zeus' Wrath hidden in a candlestick in the western tower.  It's in the room with three chests.  Bacchus' Wine in a flowerpot in the room with the dancing monk.  Hermes sandals in a pot on the left side of the throne room.
• Your party will change at the dock: [everyone will leave].

Mt Ordeal

• Don't forget to grab the Curse augment from the previous screen after the boss fight.
• If you happen to win any Cursed Rings, keep ahold of up to five.  They are useful later.

Baron

• Don't forget the chests in the weapon and armour shop.
• After the boss battle in the throne room, your party will change: [Palom and Porom will leave].
• Don't forget to go back for the Tsunami augment in the waterway.
• Don't forget to explore the basement and eastern tower for treasure chests and an elixir hidden in a candlestick.
• Don't forget the cutscene in the basement of the tower.
• Return to the Mysidian Elder for several augments.  
• Return to Mist and check the first house to the north for a golden hairpin and clothing, and then a polymorph rod and a ruby ring via a secret tunnel.  Bomb fragment in a bush in the northeast.
• Potion, two phoenix downs, hi-potion, cottage, antarctic wind, and Gaia drum in Agart town, generally hidden in bushes.
• Tent, two hi-potions, phoenix down, dry ether, 1000 gil, ether, and decoy outside in Troia town.
• Mythril knife, Mythril staff, 5000 gil, a maiden's kiss, and a diet ration in Mythril Town.

Troia Castle

• Bacchus' Wine in a pot in the basement.  Don't forget about the injured man.
• Gysahl greens scattered around Chocobo Village.
• Speak to the injured man again.  
• In your second playthrough, assign one augment, possibly bardsong, as follows: [Cid].  Ignore this in your third playthrough.

Tower of Zot

• Your party is about to change: [Tellah will leave].
• Get the Whirlwind augment from the dark elf's cave.  

Eblan Castle

• Ninja Sutra hidden behind the throne.
• In the second room in the eastern tower, Bacchus' wine hidden in a pot.
• In the west tower, there's a ninja sutra hiding in a flower pot in the room with two chests.  
• There are Hermes Sandals in a pot in the room above that which contains four chests.  
• Ninja Sutra hidden in a candlestick in the basement.

Dwarven Castle

• Your party is about to change: [Cid will leave].
• 5000 gil near the inn, Bacchus' wine in pots in the two towers, Gysahl Greens near the Chocobo nest, Bomb fragment in the room with the waters of life.  Check your bestiary with the Fat Chocobo, to make sure you trigger whichever boss you didn't get the first time at the Tower of Babel.  It will be entry 175 or 178 that you're missing.
• You can receive another copy of the Reach augment in each playthrough.  

Tower of Babel

• To complete bestiary entry 175, defeat Lugae first.  For 177, defeat Barnabas and then stop attacking and wait for the Barnabas Z form.  Do not let it self-destruct.
• Your party changes after you use the Lugae key: [Yang will leave].

Eblan Cave

• Potion in the fireplace in the infirmary.

Underground

• Three augments in the Dwarven Castle infirmary.  Achievement Unlocked: Augment Master.
• Remedy and Soma Drop at Kokkol's Forge.
• Phoenix Down and Bomb Core outside in Tomra.  Bestiary and Antarctic Wind in the room with the chests.
• Speak to the injured man in Sylph's cavern.
• You'll need to battle Asura and Leviathan in the Feymarch to obtain them as summons again. 
• Start the Eidolon search quest again.

Sealed Cave

• As you walk towards the exit, your party will change [Kain will leave].

World Map

• MP+50% augment in Mist.
• Obtain the Gil Farmer augment from the Member's Only area in Troia.
• Trade your Rat Tail for Adamantite with the tail collector
• Speak to Yang's wife in Fabul.
• Steal the Darkness augment from Odin in the basement of Castle Baron and obtain him as a summon again.
• Give the adamantite to Kokkol at Kokkol's forge
• Speak to the injured man in the house in Sylph's cave to obtain 3 augments.
• Speak to Yang's wife again.
• Inferno augment in the Cave of Eblan.

The Moon

• You can find another Level Lust augment in the lunar town.
• You'll need to defeat Bahamut again to obtain him as a summon.
• There's a face on the moon, on the northern edge of the map, just east of centre.  You can use a Dark Matter on the face on the moon to face the first bonus boss, Proto-Babil.  I would not recommend doing so at this point, as you are probably under levelled.  Don't worry, it will be there until you finish the game.

Giant of Babil

• After the four-part boss battle, you can face the second bonus boss, Geryon, by examining the square you were standing on.  I do not recommend doing so at this point.  You won't lose your chance as he will move to Mt Ordeals for the rest of the game.
• Your party will change immediately after the last battle here: [Fusoya will leave].  You will not have time to change your equipment after the battle.

World Map

• A soldier on the upper ramparts of Castle Baron will give you the HP+50% augment.
• Return to Kokkol's forge for a sword.  
• You can complete the Eidolon search quest now.  You'll get a second copy of Piercing Magic.  

Lunar Subterrane

• You'll find the Omnicasting, Bless, and Phoenix augments on the way.  
• There's a Murasame on B4 and a Masamune on B8.
• The Holy Lance is in a room off B7.
• The Ragnarok is in a room off B5.
• Do not go past floor B11 until you want to finish the game.  

Final Things

• Check your bestiary.  At this point, only entries 199 and 200 should be missing.
• From the final dungeon, you should have a full set of Crystal armour and a set of Dragon armour.  Keep ahold of them, the two Luminous Robes, Gold Hairpins, Protect Rings, any Adamant armour or Onion equipment and any Cursed Rings you happen to have found.
• At this point, my party ranged from levels 65-75.  When levelling from 71 to 100, only your equipped augments - as in, usable in battle, not including your auto-attack - will raise your stats.  
• I levelled my team against the Princess Flans, not because they're particularly efficient but because I hoped they'd drop a few Pink Tails along the way.  Even if they don't, it builds up your supply of elixirs and Dry Ethers.  I did run out of money a few times and spent time farming for Red Tails instead when that happened.  By the time my party had all reached level 99, I had a second Onion Sword but still only one Adamant Armour.

Geryon

• You can face Geryon at Mt Ordeals, by clicking on the marker at the very top.
• You'll need to be protected against elemental spells.  This is where the Cursed Rings come in.  If you're wearing any equipment which reduces elemental damage, the Cursed Ring will cause you to absorb that element instead.  You'll also need some protection against status effects.
• You can farm Cursed Rings on the first screen of Mt Ordeal.  Each battle will pit you against 4 monsters, 1-3 of them of the type with a 12% chance to drop Cursed Rings, or 24% with Treasure Hunter.  You'll have a 6% chance of winning a Cursed Ring if there are only one of the right enemies, and 18% if there are 3.  It doesn't take long to get 5.
• I gave Cecil the Crystal Mail, which protects against status effects, and the Crystal Helm, which halves elemental damage.  Adding a cursed ring meant all elemental damage was absorbed instead.  You'll still be weak against Tsunami and physical attacks, but not much else.
• Kain had the Dragon Helm and Mail, both of which halve primary elements, plus a Cursed Ring.  The Onion Shield protected him from status effects.
• I gave Edge the Adamant Armour, which protected against both status effects and elemental damage, plus a Cursed Ring.
• Rosa and Rydia had Ribbons to protect from status effects and Luminous Robes and Cursed rings for elemental protection.  This meant they only absorbed Lightening damage.  If you choose to put the Adamant Armour on one of them instead (assuming you got exactly one to earn the achievement), that leaves Edge with only a Protect Ring to halve primary elements and a Ribbon for status effects.  He cannot also equip a Cursed Ring.
• I actually defeated Geryon with most of my party around level 70.  Then I reset because Edge gained 5 levels with the wrong abilities equipped and I didn't want to waste the levels.  He was a lot easier to defeat the second time.
• Achievement: Defeated Geryon.

Proto-Babil

• You can face Proto-Babil by using a Dark Matter at the face on the surface on the moon.
• Don't worry about protecting yourself from elemental damage or status effects.
• He has 400,000HP and will begin using an attack which can wipe out your party every turn when his HP drops below 120,000.  You'll need to take him out fast at this point.  
• Darkness and Limit-Break on Kain allowed him to do 24k-32k damage, with no risk of being killed before the attack went off.  Rydia could dualcast Meteor for just under 20k damage per turn.  If Edge has Hide, he can Throw for up to 9999 damage without revealing himself until the rest of your party is wiped out.
• Having Phoenix on two characters and using salve plus elixirs to quickly replenish their MP was essential.  Phoenix will continue to go off if the characters equipped with it are at full MP.
• I raised Cecil's HP as much as possible, put Draw Attacks on him and had him defend.  This helped the rest of my team survive a bit longer.
• Achievement: Defeat Proto-Babil.

End Game

• Theoretically, Proto-Babil will be the last enemy you need for your bestiary.  Achievement: Know-It All.  In practice, as discussed above, I needed to defeat Calca before this unlocked.
• Completing the game for the second time and on hard difficulty unlocks two achievements.  Achievement: Bitter Battle, Achievement: Earth's Saviour Times Two.
• Those should be the final achievements:  Achievement: Final Fantasy 4 Master.
• This achievement did not unlock immediately for me.  I needed to close down the game and reopen it again for this one to pop.  I didn't need to reload my game.
• If you need to do a third playthrough, all instructions are exactly the same as for the second except:
• Don't give any augments to anyone but your final five.
• Don't worry about playing on hard mode, there's no further reward.