You’ll need to buy Cloud’s ultimate limit - Omnislash - with Battle Points earned from victories at the Gold Saucer’s battle arena. This will set you back 64,000 BP in disc one, and 32,000 BP later on an disc two and beyond. It’s most easily done late-game when you have more resources (the Ribbon accessory, better Materia).

Each arena bout lasts eight rounds, after which you’ll suffer a handicap randomly chosen from a slot-wheel. This can be anything from losing all your MP. to having your gear broken, being afflicted with status effects, or losing access to Materia (by color or all of it) or certain battle commands. Many of these effects can be mitigated with a Ribbon (not to mention the enemies, who will gladly debilitate you), and you’ll gain more Battle Points the more/worse handicaps you suffer.

So… being able to survive all eight rounds and endure handicaps is the key. Also, each battle costs 10 GP, which can be a pain to earn before disc two, as you’ll have to rely on the mini-games at the Wonder Square, which suck down Gil and pay out very few GP. The Chocobo races are a much, much better source of GP, but until you can race your own birds and ensure victory (one would hope), GP are likely to remain scarce. Plenty of reasons to wait before attempting this.

In disc two, during the quest to recover the Huge Materia from North Corel, stop the train from crashing into North Corel, then, after resting at the inn (courtesy of the grateful locals) enter the “house” on the ledge below the inn and talk to the lady therein. She should give you Catastophe; Barret’s ultimate limit break.

You can get this on disc two, once you’ve regained the services of a lucid Cloud from the events at Gaea’s Cliff and Mideel. Make sure Tifa is in your party and return to Nibelheim and play the following on Tifa’s piana upstairs:

Playstation Controller

X, [Square], [Triangle], R1 + [Triangle], R1 + [Square], X, [Square], [Triangle], R1 + X, [Circle], X, [Square], X

PC controls

[CANCEL], [SELECT], [MENU], [PAGE UP] + [MENU}, [PAGE UP] + [SELECT], [CANCEL], [SELECT], [MENU], [PAGE UP} + [CANCEL], [OK], [CANCEL], [SELECT], [CANCEL]

A note should pop out from a person dear to Tifa, and along with it knowledge on how to perform Final Heaven.

There is a river east of Junon that can be crossed with the buggy, inside of which dwells a narcoleptic miner. Talk to him an, if the last two digits of the number of battles you’ve fought are the same number and odd (11, 33, 55, 77 or 99) he’ll give you a piece of Mythril. He’ll also occasionally tell you how many battles you’ve fought (as well as give you a Bolt Ring if they’re even; 22, 44, 66 or 88). Just fight a battle, check back with him, repeat until you get it.

Later on, when you have the Tiny Bronco, visit a small house on a peninsula east of Gongaga - the “Weapon Seller’s” house. Talk to the man inside and give him the Mythril and he’ll let you pick between one of two chests; a large one, and a small one. Pick the small one and grab your prize from a wall safe upstairs; the Great Gospel.

Open the locked safe in the Shinra Mansion in Nibelheim, then defeat the Lost Number boss, who will drop Cosmo Memory - Red XIII’s ultimate limit break. Easier said than done. Even though it’s been covered in the walkthrough and under the “Wont You Be My Valentine?” trophy, it’ll be covered again here, just so you don’t have to scroll around too much:

Go to the Shinra Mansion in Nibelheim, which can be done any time after Cosmo Canyon. Search the note on the ground in the small room just left of the entrance to find some clues:

• Dial (1) “The lid of the box with the most oxygen.”

• Dial (2) “Behind the Ivory’s short of tea and ray.”

• Dial (3) “The creek in the floor near the chair on the second floor… then to the left five steps, up nine steps, left two steps, and up six steps.”
  That’s right, you need to open a safe, and to do this you’ll need to find all its dial posisitions. The first is on the note itself, just scroll down past the dial (3) option to find a hidden fourth option, which, when selected will give you (4: Right 97). One down, three to go:

• From the entrance head north through a doorway under the stairs, then turn left to find a large room with a piano. Search behind the piano to find (2: Left 10).

• Return to the entrance room and head upstairs, then take a left to reach a circular greenhouse. Open the chest to obtain an Enemy Launcher. Search the chest again to discover (1: Right 36).

• Finally, return back right to the main room, then - staying atop the balcony - run to the right wing of the mansion. You’ll immediately find yourself in a hallway running mostly north-south. Walk along the left side of the hallway and just keep hitting [X] until you locate (3: Right 59).
  Now that you have all the codes, return to the left wing of the mansion and go into the room north of the circular greenhouse to find a safe. You’ll have to enter the codes, in order, going the right direction, within twenty seconds. Yikes. So, go right to 36, then left to ten, back right to 59 and finally go right to 97. Do it fast enough and you’ll open the safe, freeing a Basement Key and some Odin Materia… and the Lost Number boss. Defeat it (see the walkthrough for more information on how to achieve this feat, if necessary) and it’ll drop you Red XIII’s ultimate limit break; Cosmo Memory.

Visit Wutai for the first time and complete the stolen Materia side-quest, then after you have the Highwind in disc two, return there with Yuffie in your party and enter the pagoda. She’ll have to win four one-on-one boss battles to conquer the pagoda. The last boss you face will drop All Creation - her ultimate limit break. This is also how you obtain the Leviathan Materia and unlock the “Making Waves” trophy.

The most uninspired ultimate limit break for the most uninteresting character in the game; just use Cait Sith’s Dice limit break until this unlocks.

You can get this on disc two, once you’ve regained the services of a lucid Cloud from the events at Gaea’s Cliff and Mideel. Make sure Vincent is in your party and you have either a) the submarine or b) a Green Chocobo. There is an elevated circular lake surrounded by mountains south of North Corel, east of Nibelheim. Feeding this lake is a waterfall, behind which is a cave, which you can enter by running into the waterfall’s left side on the world map. If Vincent and Cloud are in your party, a figure from Vincent’s past will be there, and some backstory will be revealed. Leave the cave and fight about ten battles, then return and search the spot where the figure stood last time you were here to obtain Chaos (Vincent’s ultimate limit break), and Death Penalty (Vincent’s ultimate weapon).

After you obtain the submarine, dive and search the eastern coast of the western continent to find a crash plane; the Gelnika. On board are some of the strongest monsters - and some of the best gear - in the game. In the large cargo room (the one with a ruined helicopter) you can search a treasure chest along the southern end of the screen. It’s nearly undetectable until it’s opened, though, so just search the area south of the helicopter at the bottom of the screen until you find it. It contains Highwind… no, not the vehicle, Cid’s ultimate limit break.

Beat the game. There’s a whole walkthrough out there telling you how to best go about this. That’s one thing that won’t be rehashed here. Heh.

There are two ways to get this; one is to defeat one of the strongest foes in the game, the super boss Emerald Weapon, which will drop an Earth Harp. Take it back to the old man in Kalm (on the second storey of a house just right of the stairs leading up to the shops) who will give you one of each type of Master Materia.

The other it to recover all the Huge Materia intact, then have made sure to pick up all the Summon Materia in the game. If you’ve mangaed to do those two things, you’ll then only have to master every. Single. One. Of. Them. Grinding Magic Pots and Magic Balls in the North Cave with double and triple AP weapons equipped is the only sane way to do this. The Summon Materia you’ll need, and their locations, can be found below:

Alexander

Not missable. Oh boy. This one is a bit of work just in itself. In the Great Glacier area (the huge sheet of ice north of Icicle Inn), you can find a Hot Spring area. While there touch the Hot Spring, then head out to the Blizzard Tundra and run east as best you can until you reach the eastern end of the Blizzard Tundra, at which point you’ll transition to several barren diagonal junk screens. Run down them until you find a cave, inside of which you’ll find the Snow Witch. Talk to her and she’ll react violenty to the Hot Spring odor your brought into her home. Kill her and she’ll drop the Alexander Materia.

Bahamut

Missable. Defeat the Red Dragon boss in the Temple of the Ancients, then pick up this Materia. This is also the subject of the “Waiting in the Wings” trophy.

Bahamut ZERO

Missable. The subject of the “Bahamutype-0” trophy, to get the Bahamut ZERO Materia you’ll need to recover all the Huge Materia. This includes the Huge Materia at North Corel, Fort Condor, the Junon Underwater Reactor and Rocket Town. Once you have them all, they’ll be stored in Bugenhagen’s observatory in Cosmo Canyon. Use his lift to reach them and investigate the blue Huge Materia, then select the option “Get closer…”. If you have the Bahamut Materia (dropped after defeating the Red Dragon boss) and the Neo-Bahamut Materia (found lying on the ground in the Whirlwind Maze before the Jenova-DEATH boss battle) you’ll be rewarded with Bahamut ZERO.

Choco/Mog

Missable. On your first visit to the Chocobo Ranch (or no later than the end of disc one) talk to the Chocobos residing in the pen outside and respond by saying “Wark”. They’ll do a little dance, and you’ll get this Materia. They’ll be gone later on in the game, so be sure to do this early.

Hades

Not missable. You can find this in the cargo room of the Gelnika, hidden on the ground near the helicopter.

Ifrit

Missable. On the voyage across the sea from Junon to Costa del Sol, after you defeat Jenova-BIRTH, grab this Materia off the ground. Once you leave the room, you can’t go back and get it.

Knights of the Round

Not missable. Breed a Gold Chocobo (check out the walkthrough, the Chocobo Breeding Guide or the details under the “Roundtable of Destruction” trophy for more info about this) then ride your golden new bird to an unmarked, secluded round island (named Round Island, in fact) along the north-eastern end of the world map. You’ll find this materia in a cave.

Kujata

Not missable. In the Sleeping Forest that connects Bone Village to the City of the Ancients, you’ll see flashing red lights moving around. Catch them (hit [X] on them) and you’ll get the Kujata Materia.

Leviathan

Not missable. The subject of the “Making Waves” trophy, also part of getting the “Meet Your Maker” trophy. Visit Wutai for the first time and complete the stolen Materia side-quest, then after you have the Highwind in disc two, return there with Yuffie in your party and enter the pagoda. She’ll have to win four one-on-one boss battles to conquer the pagoda. Once done, the last boss will give you the Leviathan Materia.

Neo Bahamut

Missable. In the Whirlwind Maze (the area after scaling Gaea’s Cliff) you can find this materia just… lying on the ground, sometime before the battle with Jenova-DEATH.

Odin

Not missable. Open the safe in the Shinra Mansion in Nibelheim, then defeat the Lost Number boss. After the fight, this materia will be lying on the ground, just waiting for you. In case you forgot how to unlock this safe, or you’re too lazy to scroll around… here, have some redundancy:

Go to the Shinra Mansion in Nibelheim, which can be done any time after Cosmo Canyon. Search the note on the ground in the small room just left of the entrance to find some clues:

• Dial (1) “The lid of the box with the most oxygen.”

• Dial (2) “Behind the Ivory’s short of tea and ray.”

• Dial (3) “The creek in the floor near the chair on the second floor… then to the left five steps, up nine steps, left two steps, and up six steps.”
  That’s right, you need to open a safe, and to do this you’ll need to find all its dial posisitions. The first is on the note itself, just scroll down past the dial (3) option to find a hidden fourth option, which, when selected will give you (4: Right 97). One down, three to go:

• From the entrance head north through a doorway under the stairs, then turn left to find a large room with a piano. Search behind the piano to find (2: Left 10).

• Return to the entrance room and head upstairs, then take a left to reach a circular greenhouse. Open the chest to obtain an Enemy Launcher. Search the chest again to discover (1: Right 36).

• Finally, return back right to the main room, then - staying atop the balcony - run to the right wing of the mansion. You’ll immediately find yourself in a hallway running mostly north-south. Walk along the left side of the hallway and just keep hitting [X] until you locate (3: Right 59).
  Now that you have all the codes, return to the left wing of the mansion and go into the room north of the circular greenhouse to find a safe. You’ll have to enter the codes, in order, going the right direction, within twenty seconds. Yikes. So, go right to 36, then left to ten, back right to 59 and finally go right to 97. Do it fast enough and you’ll open the safe, freeing a Basement Key and some Odin Materia… and the Lost Number boss. Defeat it (see the walkthrough for more information on how to achieve this feat, if necessary) and pick up the Odin Materia off the floor.

Phoenix

Missable. Successfully defend Fort Condor from Shinra’s soldiers during the Huge Materia quest in disc two (previous Fort Condor battles don’t matter) and go investigate what happened to the condor on the roof. You’ll find this materia lying around.

Ramuh

Missable. After defeating the boss in Corel Prison, Cloud will be picked to race for everybody’s freedom. No pressure. In the Chocobo jockey’s lounge before the race you can find this materia sitting on the ground in front of some stalls. If you don’t pick this up before winning the race, you’ll never get a second chance. Again, no pressure.

Shiva

Not missable. During your first visit to Junon you’ll have to fight the boss Bottomswell, after which you’ll have to give Priscilla CPR. Succeed (you can’t fail) and when you’re forced to talk to her later (awkward…) she’ll give you an amulet, which just so happens to contain the Shiva Materia.

Titan

Not missable. Search Gongaga’s ruined reactor to find the Titan Materia.

Typhon

Not missable. In the Ancient Forest area, during the part where you have to use the tongue plants to reach higher branches, travel all the way to the right (using a trio of tongue plants in succession) to reach a far branch, on which is an item bag, which just so happens to be this materia.

Near the end of disc two you’ll have to defend Midgar from Diamond Weapon. He’s easily the weakest Weapon you’ll fight in the game, just use Knights of the Round to defeat him in one shot, or pummel him with Trine spells. Just don’t use Limit Breaks on him to avoid his one powerful counterattack.

Ruby Weapon is the strongest foe in the game, and the best way to tackle it is arguably by casting combinations of Hades (to stun it) and Knights of the Round (to deal damage). Be wary, however, as he’ll counter summons with Ultima if he’s not stunned. Physical attacks do little damage to it. Full details on preparations and tactics for this super boss can be found in the Emerald and Ruby Weapon section of the guide.

The other super boss of the game (Ultimate Weapon is too weak to count), Emeral Weapon isn’t as difficult to defeat as Ruby Weapon. You can use physical or magical attacks, but double-casting Knights of the Round (with W-Summon Materia) and then using Mime with your entire party will do the trick. It’ll take half of forever, but it’s still doable in the time limit. You can find detailed preparation advice and tactics for this boss in the Emerald and Ruby Weapon section of the guide.

Surely you don’t need help with this one… right?