• Break Damage Limit
• Triple OVerdrive
• Double AP
• One MP Cost
When you get to the Calm Lands, go to the Monster Arena. Talk to the man there, and he'll ask you to catch fiends for him. Buy the catching weapons, defeat the fiends with them, and they're caught. You only need at least 1 of each species of fiend in the Calm Lands, and there are 9 total. I'd give a list, but I can't be bothered to remember right now.
Once you've caught all 9 species, talk to the man. He'll say he created a new monster, and you can fight it if you want but it's not necessary for this. Talk to him again and a treasure chest will appear but it can't be opened. Inside of that is the Nirvana, and you need the Cloudy and Celestial Mirrors to open it.
Cloudy Mirror
Somewhere in the Calm Lands is a person sitting on a Chocobo. Talk to them and ride a Chocobo. Then, look at the map and go all the way up to the entrance to Macalania. On the map is a small island-type piece of land, and if you walk over towards it you'll see a Chocobo feather. Push the X button, and your Chocobo will fly you down. Now you've found Remiem Temple.
On each side of the outside of the temple are Chocobos. Go to the left, and examine the sphere lying on the ground. It'll explain that the Chocobo there is a champion and the challenger is on the other side. Yep, you've gotta race, but it's really not difficult at all. So, go to the other side of the temple, talk to the Chocobo (yes, talk. They have ears, you know.) and thus begins the race. Just go down towards the circular area at the bottom before the other Chocobo and your prize is the Cloudy Mirror.
Celestial Mirror
This could seem complicated, but it's not at all. It only takes a few minutes, and then you can get the Nirvana--as well as the other weapons.
You need to go to Macalania. I'm pretty sure that the Airship takes you to the Travel Agency, so you need to go down the glitter path to the main entrance (Macalania - South). There, close to the Save Sphere, is a woman and a boy. And so begins this little quest.
1. Talk to the woman, and she'll say that her husband was supposed to meet her and their son there.
2. Go to the right and to Macalania Woods - Campsite (it's across from the Spring, and I'm sure you know where that is.). There'll be a man there, talk to him. You'll have the option to tell him where his wife and son are or not, and if you want the Celestial Mirror you need to tell him where they are.
3. Now go to the main area once again, Macalania - South, and you'll see the husband and wife there. Talk to them, and they'll say that their son is missing. *eyeroll* Man, they're not good at keeping track of each other, are they?
4. Head up the glitter path, and at the intersection go north until you see the boy standing in front of a large, spherical crystal. Examine the crystal, and it'll ask you to hold up the Cloudy Mirror. Do so, and it'll turn into the Celestial Mirror.
Now, go to the Calm Lands, examine the chest, use the Celestial Mirror, Yuna will show up and you'll open the chest. And now you've got the Nirvana. But there's no point in using it now, because it's only ability is 'No AP.' So now you have to power it up.
Moon Crest
The Moon Crest is very easy to get, and you can get it very early on in the game. All you have to do is go to Besaid Beach and swim in the ocean until you find land with a treasure chest. Open it, and in there is the Moon Crest.
Moon Sigil
This is a bit harder to obtain, as are all of the Sigils. What you have to do is obtain every Aeon, battle Belgemine's Aeons at Remiem Temple, and once you do that you get the Sigil. Of course, I'm going to explain how you do all of that.
Now for another 80 steps just to get the Magus Sisters to fight Belgemine (I almost typed Namine... Man, this is FFX not KHII!!) and obtain the Sigil. You need to get Yojimbo, Anima, and the Blossom Crown and the Flower Scepter to open the seal on the Chamber of the Fayth in Remiem Temple. Yeah, this can be a real pain in the ass, but it's worth it.
Go to the Chamber of the Fayth and Yojimbo will ask you what you want him for. Answer, "To defeat the most powerful enemies" and he'll give you his offer. You can haggle with him, pay him more or less or whatever. If you triple his offer, though, he gives you Teleport Spheres and a higher chance at getting him to do Zanmato. In any case, you get Yojimbo--and you have to pay him to attack. Kind of useless in my opinion, but hey, you need him nonetheless.
In any case, you have to find Baaj Temple--you were there in the beginning of the game, it's the place Tidus ended up at after Zanarkand got destroyed. Talk to Cid on the airship to open the menu, and go to 'Search.' You'll see a giant map, an arrow, and numbers and letters on the left side of the screen. Those are the coordinates, and yeah, you need to know them, so here they are...
X Coordinate: 11~16 (any number between those two)
Y Coordinate: 57~63 (any number between those two)
The coordinates are always different, but they are always between those numbers so just fiddle around and pay attention to the numbers and you'll find it. Now go there. But of course, there's a catch, right? You have to fight that cage-resembling fiend that tried to kill Tidus in the beginning, and you only have Rikku, Wakka, and Tidus to do so. So equip them well, jump in the water, and head towards the entrance of the temple. Defeat the fiend (and good luck, because it can be difficult with its Stone Punch, KO Punch, and the attack where it inhales one of them.) and head into the temple.
You'll find yourself at a small hall with six statues. Go up to all of them and if they light up, then you got the item from there. If one doesn't light up, you have to go back to that temple. Honestly, I'm not sure which is which. Some are obvious, and some are not, but just do your best to figure it out. In any case, once they all light up you can enter the Chamber of the Fayth.
I'm not gonna spoil who the Fayth is, but she'll give Yuna her Aeon, and now you've obtained Anima.
Blossom Crown
To get this, you need to capture at least one of each fiend in Mt. Gagazet--on the slope and in the cave, and under water as well. And yes, to make it easier on you, I'll give you a list.
1. Bandersnatch - Black dog
2. Ahriman *Cave* - Flying Eye
3. Dark Flan *Cave* - Giant purple flan
4. Grenade - Purple Bomb
5. Grat - Seed-pelting plants
6. Grendel *Cave* - Four horned thing, appears with the Ahriman usually.
7. Bashura - Purple Ogre
8. Mandragora *Cave* - Ochu
9. Behemoth *Cave* - Giant purple muscle thing (you can steal Ethers from it)
10. Splasher *Underwater* - Pirhanas
11. Achelous *Underwater* - Bird-like jellyfish
12. Maelspike *Underwater* - Shark things
There are two other fiends that appear on Mt. Gagazet, an Imp and Nidhogg but you don't need those, as those are also found in the Cavern of the Stolen Fayth and when you catch them, they go under the 'Sunken Cave' list at the Monster Arena, so you don't need to catch those two for this. You should catch them anyway, though xP
Anyways, after catching all of those, head to the Monster Arena, speak to the man and he'll give you the Blossom Crown. I think he'll also give you Three Stars x60 if you talk to him after that, which you can use to get One MP Cost.
Flower Scepter
Yes, there's more, but this is the last part of it! So, why stop now?
You had better know where Remiem is, because I'm too tired to explain it all over again. It's up above somewhere if you forget.
Talk to Belgemine, fight her Aeons, and after you defeat Bahamut you'll get the Flower Scepter. You can continue and fight Yojimbo and Anima after that, but you still have to get the Magus Sisters before you get the Sigil.
Go to the glittery pink thing behind Belgemine and use the two items. These will break the seal, and Yuna enters the Chamber of the Fayth and emerges with the Magus Sisters.
Now, fight Belgemine's Magus Sisters (it's not that difficult, really, but I recommend using Bahamut or Anima--or both, if one of them dies). Once you defeat them, you'll have the option to Perform the Sending or not. PERFORM THE SENDING, and you'll obtain the Moon Sigil.