To prepare, start training vigorously from the time the game starts to the time you get to the Spherimorph (about ten fights minimum in each area). You should have about 15000 gil or more when you are ready. Go to O'aka and ask for weapons. Leave, then he will ask you about the prices. Tell him that they are too expensive, then go back and buy weapons. The prices should be lowered to some extent. Buy the Sonic Steel for Tidus, Rod of Darkness for Yuna, and the Force Knuckles for Rikku. When you get to the part of the Macalania Woods where you fight Spherimorph, immediately save if you are uncertain that you can defeat it. To fight Spherimorph you should equip the following recommended items. Tidus (Sonic Steel, any armor with Magic Def 3or 5%), Yuna (Rod of Darkness or Laevatein, Seeker's Ring; HP + 10%), Wakka (Switch Hitter, Emerald Armguard), Lulu (Fatal Cait Sith or Water Moomba, Seekers Bangle), Auron (Shimmering Blade, Recovery Bracer), Rikku (Force Knuckles, NulBlaze Target), Kimahri (Hunters Spear, Red Armlet). Start the fight with Tidus, Auron and Wakka. Tidus goes first, so set the tone with his Overdrive (if he has it). Do not use Wakka's Overdrive because it is elemental and will heal Spherimorph. Instead, use a physical attack. Use Auron's Magic Break to weaken spells, then switch in Kimahri and use his Jump or Seed Cannon Overdrives (if he has them). Use Yuna and summon Ifrit. Use his physical attacks to damage Spherimorph. Spherimorph will attack with Fire, thus healing Ifrit. Switch out Ifrit and use normal characters occasionally. Switch Ifrit back in and use his physical attacks until Spherimorph starts using its physical attacks frequently. Dismiss Ifrit and use Auron's Power Break to weaken its physical attacks. Then, finally pummel it down with either Ixion or Ifrit's physical attacks, occasionally healing them with elemental spells.

Have Tidus, Lulu, and Yuna on your team. Use Yuna to cast the Nul spells, then use Tidus' attack. Spherimorph will cast an elemental spell on Tidus. However, if you used the Nul spells it will not harm him. Have Lulu cast the opposite of that spell/ Spherimorph will then use Elemental Shift. Keep repeating this and Spherimorph will soon be dead and you will suffer no damage.