The team will reach the Macalania Woods after traveling through the Thunder Plains.
Have Tidus walk towards Auron to continue with a few more cutscenes. Tidus will admit to Auron that he is worried about Yuna, but Auron is convinced that Yuna has something up her sleeve. Move forward to catch up to the group after speaking with Auron.
Make use of the nearby Save Sphere and save your game before you do anything. The fiends within Macalania Woods are Water-based. This is completely the opposite of the fiends you were fighting in the Thunder Plains.
Switch our your weapons, removing any that had the 
Waterstrike ability and adding in any that have the Lightningstrike ability. Switch your armor to any armor that has the Water Ward or Waterproof abilities to make the upcoming fights much easier (and only if you happen to have already found these items as random loot). This means that you should also be removing Tidus’ powerful 
Brotherhood sword for this part of the game.
The team will head along the pathway that leads up into the trees; follow them in that direction.
Just around the corner is a hidden treasury chest that contains 
Sleepy Cait Sith weapon for Lulu. Further down the pathway is another treasure chest which contains 2,000 gil.
Go up the tree branch which leads in to the next area.
Continue along the pathway until you reach the furtherest northern point on the map and you will find a treasure chest lodged in behind a tree. Open it up to obtain three 
Phoenix Downs.
You will run into Barthello once you get far enough along the bottom of the pathway in this area.
You can learn the “Aqua Breath” Ronso Rage ability by having him use 
Lancet on a Chimera Brain enemy in this area. Check out the Overdrive section for more information on Kimahri’s Ronso Rage.
Barthella will ask the team if they’ve seen Dona. Apparently the two of them were separated on their way through Macalania Woods. Auron will tell him to remain cool and continue to search. Continue down the path after the cutscene.
Just up ahead is where you can participate in the Butterfly Catcher mini-game. A strange creature will explain that a “Butterfly with rainbow wings will lead the way to secret things”. You should skip the hunt for now.
Failing this mini-game will throw you in to a battle against a fairly challenging fiend and you can’t use the reward, which is the 
Saturn Sigil, to create Kimahri’s Celestial Weapon, the 
Spirit Lance, until much later in the game.
Therefore, you are welcome to attempt this challenge if you prefer but it is not necessary or recommended at this stage of the game. Click on the link below for more information:
The pathway in the next area is completely straight with no turn-offs so you can’t get lost. There is a treasure chest along the way behind a tree that contains a 
Remedy.
Save your game at the Save Sphere before you continue as there is a boss battle coming up. Buy any items that you may be running low on from O’aka XXIII who is just a little further down the pathway. This is the first time that 
Hi-Potions will be available for purchase within the shop so stock up if you need them.
Start off by entering his shop and then exit the shop. He will ask you if you think the prices are either too expensive, too cheap or just right. Select “too expensive” and he will drop the prices.
The closest path on the right side of the screen is currently blocked off. It does not lead anywhere and does not come into play until later on in the game.
That being said, there is an 
Al Bhed Primer (Vol. XV) that you will want to pick up part way down the path. Use the screenshot below to help you find it.
Continue north to meet up with the rest of your team. Auron will stop you part way along the trail and insist that they head off into a secret area of the woods. While there, they will be ambushed by the next boss.
Walk forward to initiate another short cutscene and the next boss battle.
HP: 12,000
It is important to understand the mechanics of this boss battle as this knowledge will make it much easier to defeat Spherimorph.
Spherimorph changes and rotates the elements that it attacks with and that it is weak to during the battle. For example, is Spherimorph is attacking with Fire-based spells, it will also be weak to Ice-based magics. Recall the different weaknesses:
Just attack Spherimorph with a regular “Attack” to find out what element Spherimorph is currently using and currently immune to. Spherimorph automatically counters each attack with a weak magic spell.
You will want to start off by immediately adding Lulu into your party to start utilizing her magic attacks. Use Auron’s 
Magic Break ability to weaken the attacks Spherimorph will be using against you if you have it as well.
Yuna’s Nul spell, such as 
NulBlaze, NulShock, NulTide and NulFrost work as excellent preventative measures to absorb magic based attacks.
The strategy is to use one character to attack and find out what element Spherimorph currently is (likely Tidus). Swap out Tidus’ weapon if it has any elemental based attack ability as this will cause it to heal the boss from time to time. Use Yuna to heal up Tidus while he attacks and use Lulu to spam elemental spells until you defeat Spherimorph.
Steal:
Ether (common)
Turbo Ether (rare)
Drops:
Lv. 2 Key Sphere
You will obtain a Jecht’s Sphere at the conclusion of the battle. Obtaining Jecht Spheres are how you add to Auron’s Overdrive abilities. Check out the Overdrive section for more information. This Jecht Sphere will teach Auron the Shooting Star ability.
You need to obtain all of the Jecht Spheres in order to learn Auron’s Overdrive abilities, however, if you get too far in to the game (namely, after you have obtained the Airship, a number of the previous locations in the game will be blocked off by Dark Aeons which appear later in the game.
Therefore, it is advisable that you take this opportunity to return to a few of the previous areas that you have explored, including Besaid Village, the S.S. Liki, Luca, the Mi’ihen Highroad, Mushroom Rock Road and the Moonflow to pick up some Jecht Spheres that have now appeared.
Note that the critical Jecht Sphere to obtain is the one in Besaid Village as this area will be blocked off by Dark Valefor. The rest are just bonuses that you can pick up during your travels back to Besaid Village. Click on the “Jecht Sphere” link below for more information.
This is the time where you would now consider returning to some of the previous areas to obtain a few Jecht Spheres that have appeared. These are required in order to obtain more of Auron’s Overdrive moves. Check out the Jecht Sphere section below for more information:
Auron has more things to say to Tidus before you can leave the area, but afterwards, make sure that you save at the Save Sphere before you proceed. The Save Sphere is just south of where Auron broke through the pathway. Go north once you are ready.
The next phase of the game takes place near another Rin’s Travel Agency location at the frozen Lake Macalania. You may need to travel back here on foot if you decided to go back and search for all of the Jecht Spheres. Go north from this area (where O’aka XXIII was standing) and in to the next zone.
