The Fastest Way to Get Power Spheres in "FFX"by Matthew Anderson ; Updated September 22, 2017
Power spheres activate the strength, defense and hit point nodes on the Sphere Grid in “Final Fantasy X.” Initially, players should have little trouble finding enough power spheres to develop all seven characters. Later in the game, players get the ability to replace attribute nodes on the Sphere Grid with more potent versions. This is required to reach the maximum value for each attribute. A player could potentially need thousands of power spheres to activate all of the new nodes for all seven characters.
Equip all of the characters in your party with weapons with the “Catch” ability. You can purchase these weapons at the Monster Arena in the Calm Lands.
Go to the Mi’ihen Highroad.
Capture a Mi’ihen Fang, Ipiria, Floating Eye, White Element, Raldo, Vouivre, Bomb and Dual Horn. All you have to do to capture a monster is kill it using a weapon with “Catch” on it. Defeating the enemies on the Mi’ihen Highroad is trivial by the point you can get “Catch” weapons.
Go to the Monster Arena.
Re-equip the weapons you normally use for combat.
Choose Kottos to fight from the monster list in the arena. He is unlocked after you capture at least one of each of the monsters listed in Step 3. It costs 6,000 gil, the currency of the game, to fight him.
Use a Power Distiller on Kottos. This changes all of the items he normally drops into power spheres.
Cast "Protect" on each of your party members. All of Kottos' attacks are physical, so this negates a large part of his damage.
Use "Sentinel" with whatever character has the highest defense. This causes Kottos to attack only the character using "Sentinel" and further reduces the amount of damage Kottos can do.
Use your most powerful attacks with your other two characters. Kottos has no special weaknesses or resistances, so there are no specific attacks that are more useful for defeating him.
Kill Kottos with an attack that does at least 15,000 more damage than his remaining HP. It is useful to save an "Overdrive" attack on one of your characters for this. This causes an overkill to occur. Kottos usually drops 40 power spheres. On rare occasions, he only drops two power spheres.
Repeat Steps 6 through 11 to get as many power spheres as desired.
Due to how the Sphere Grid system works in “Final Fantasy X,” it is very difficult to predict how powerful enemies are in relation to your characters. The only effective way to determine if you are prepared is to fight Kottos and see how difficult it is. Unlike most fights, the game does not end if you lose a fight in the Monster Arena. All you lose is the minor 6,000 gil fight fee.