As you attempt to enter the Mount Gagazet the Ronso clan will stop you, and tell you that because you are a traitor of Yevon you may not pass. Yuna will convince them that her intentions are good, and the Ronso’s will agree to let her pass.
Kimahri is going to fight Biran and Yenke very soon, and they both have Lv. 3 Key Sphere’s which you can steal from them, so make sure Kimahri knows steal. Either use a Special Sphere, or a friend Sphere to get it if you don’t have it, and then proceed up the mountain.
Two very important aspects of this battle:
1) Make sure you steal from both of them.
2) Make sure you use Lancet on them until you have all of the moves you can learn from them, as they have quite a lot. Biran in particular.
Other than that it’s just a regular battle. Be sure to keep Kimahri’s health up using Hi-Potions and X-Potions, and then use overdrives to take the two Ronsos out. Yenke is weaker, so I suggest taking him out first. If Biran and Yenke guard each other to stop your attacks just wait until they split up which is when one of them does the Bulldoze attack.
After you school them you and your party (including Kimahri) will be aloud to pass. Continue up the mountain and you’ll get to hear the Ronso’s sing the Hymn for you. Now, after all that, you can be on your way, because this is going to take a while. You now get to trek across the mountains, and it’s no short trail. Along the way you’ll encounter several monuments that mark the graves of Guardians who failed to complete the pilgrimage. If you stop at each of them you’ll get a little more background on summoners and their pilgrimage. A Braska Sphere can be found far up north. Along the way you’ll also meet Wantz, who will tell you that the Yevonites had imprisoned O’aka. He will also tell you that he is now going to take O’aka’s place. You’ll know when you’ve reached the end because there will be one last save sphere before you move onto the next screen, and I suggest you level up because the next boss can be rather difficult. Again, if you have to much trouble with the next boss then try to get Yuna’s overdrive before you battle Seymour and then blast him with a Mega Flare to start the battle.
A little ways up in the next screen Rikku and Tidus will have a talk about their plans on stopping Yuna from obtaining the Final Aeon. They basically come up with the conclusion that they have to wait longer, because neither of them has come up with a plan yet. The two of them will then spot Seymour off in the distance. The party will then rejoin to fight Seymour in his new form:
Seymour flux: can be terribly difficult if you don’t know what your doing. The main move you need to watch out for is Total Annihilation. Seymour will charge up, and then use this move next, and your likelihood of surviving is very low, because it can do up to 5000 damage per character. Get an Aeon out if you can predict it coming. Mortiorchis, Seymour’s little buddy (who’s back again) will cast reflect on Seymour which you should dispel as soon as you can, and you should also make sure to Haste/Hastega your team so you can get as many moves in as you can before Seymour Annihilates you. He will cast Flare when his health gets low, so if your quick to dispel him and he casts it on himself (which he always does for some dumb reason) he will hurt himself. Again, a nice Aeon overdrive obtained and stored before the battle can really help seal the battle for you.
After the battle the team will continue their journey to Zanarkand. After they’re finished talking you can make your way east.
Now you’ll see a gigantic wall with a bunch of fayth, all sending their energy to one source. When Tidus touches it he will be transformed into a dream. I won’t ruin the story for anyone who’s just reading, so you go ahead and play through this one.
After Tidus’ little dream you can continue down the path, where you’ll arrive in a cave.
Gagazet Mountain Cave
Keep following the same trail through the cave until you come across a save sphere where the path splits in two, and start by going down the left path. Go a little ways down and you’ll arrive at a pool. From here forward, at least for this part of the cave, you will only be able to use Tidus, Rikku and Wakka, as they are the only players you can use underwater. Follow the cave trail all the way to a fork in the road, where you should turn and go left again. Now you’ll have to run down the path until you reach a glowing orb surrounded by a guard. It’s The First Trial of Gagazet. All you have to do is hit the glowing orb with Wakka’s ball to proceed. Just throw a little before the gap in the guard appears to hit the orb. Once you do it successfully you can run up and grab the chest for a Lv. 1 Key Sphere.
Now go back to the first fork in the road, before the pool, back where the save sphere was. Once you get up the stairs take a left and go down that path. When you get to the split in the path go right and enter the pool. Keep going until you reach the end of the path, where you’ll find yourself staring at three lit up circles on the wall. They make up the Second Trial of Gagazet. All you have to do is stick the "correct sized person" into each hole. The colors match with each characters Sphere Grid color. Rikku is Green, Tidus is Blue and Wakka is Red. You reward in front of the circles is a Fortune Sphere. Go back down to the save sphere. Make your way back to the First Trial of Gagazet, and not to far up ahead you will see a new accessible area off to your right that leads to a chest which contains Pep Talk, a shield for Wakka.
Now go back to the save point, up the stairs, and this time take the path to your right. Go all the way down the path to arrive at two chests that you could not retrieve earlier. Once contains a Recovery Ring for Yuna and the other contains a Return Sphere. Now, from the stairs, go left again but this time when you come to the split in the road go down the left side. You will notice that there are some steps there that weren’t there before. Head up them to exit the cave. At the top you’ll get to see a scene between Auron and Yuna.
Sanctuary Keeper: Now you get to battle the Sanctuary Keeper. He is one tough boss. He uses all the moves you wish didn’t even exist. First of all he has Photon Wings, which can cast a variety of abnormal status effects on you and deal quite a bit of damage. He also has numerous physical attacks that deal up to 2500 damage, and some that hit multiple party members. The thing to watch out for is his ability to heal himself both of abnormal status effects and of regular HP. I suggest you cast Reflect on him so his curative spells not longer work, or else you could be fighting for a very long time. He’s pretty smart though, and he may cast reflect on you. This will allow him to cast spells on that party member to in turn have it effect him, like Curaga for example, destroying the effect of having Reflect cast on him. He is resistance to Physical and Magical attacks, so just nail him with everything you got. Cast Haste, use Armor Break, and then nail away till the cows come home. Aeons really help too.
Afterwards Rikku will attempt to convince the team to stop and rest so she can think of a way to avert Yuna using the Final Aeon. Then Tidus will have second thoughts too, and Auron will tell him about how he once thought just like him. Continue down the road when you’re done. As you go just a little ways up you’ll get a view of Zanarkand as it is now, decimated.
As Yuna and Rikku have one last talk Yuna will drop a sphere. Take a look at it before you continue to see a video of her saying her last words to all the party members. Finish going up the mountain after the video is done. You’ve finally arrived at the Zanarkand Ruins.