This section of the strategy guide is intended to be used when you’ve reached the end game content for Final Fantasy X.
Many of the strongest enemies and bosses in the game will require you to completely level your characters through their Sphere Grids. This method is for power leveling your characters and is not meant to be used if you’re just having trouble defeating one of the story bosses.
This leveling technique focuses on three auto-abilities, an Overdrive mode setting and battling one specific fiend, the Don Tonberry, in the Monster Arena. The three auto-abilities that you will be using are:
Triple AP
Triple Overdrive
Overdrive → AP
Make sure that you also have your characters equipped with armor that has the Auto-Phoenix auto-ability so that you can revive your characters as they are KO’d.
With weapons that contain all three of these auto-abilities, you then need to set your character’s Overdrive mode to “Comrade” which will cause their Overdrive gauge to fill when their allies take damage.
Alternatively, if they do not have the Comrade Overdrive Mode, you can use Stoic as well. Check out the Overdrive Modes section below for more information:
You will need to obtain the weapons for starters. You can go about customizing them yourself, but there is actually an easier method for getting started. Check out the guide for obtaining Triple AP weapons below:
The weapons you obtain through this method will have just one of the auto-abilities that you need. You will need to customize the other two abilities and add them to the weapons.
Triple Overdrive can be added by obtaining 30 
Winning Formula. You can obtain these by defeating Ultima Busters in the Monster Arena. Alternatively you can customize the Double Overdrive auto-ability, though it won’t be as fast. Double Overdrive can be customized by obtaining 30 Underdog’s Secret which can be obtained as a Monster Arena reward or by defeating a Th’uban.
Finally, you will need to add the Overdrive → AP auto-ability. This can be obtained by picking up 10 Door to Tomorrow which can be obtained by defeating Bomb Kings in the Monster Arena.
With your weapons in hand, your armor that has the Auto-Phoenix auto-ability, a healthy compliment of 
Phoenix Downs, you are now ready to fight Don Tonberry.
Each time you attack Don Tonberry it will use a move called Karma. Karma will inflict damage based on how many enemies that specific character has killed. The formula is “the character’s kill count” multiplied by 100. If your character has defeated 1,000 enemies or more, Karma will do 99,999 damage.
You need to have a character attacking that will cause Don Tonberry to do 99,999 damage in your party. Have them attack Don Tonberry - they will be killed, but this will cause each of the other party member’s Overdrive gauges to fill which will be converted into AP. After a few attacks, you can use the Flee command and exit the battle, and you will get to keep the AP.
This method will make it easy for you gain AP quickly. In fact, at the end of each battle, each of your characters will likely have 99 Sphere Grid levels (the maximum available).
This method is part of the steps you will need to take if you wish to maximize your characters levels and stats. Check out the stat maxing guide below for more information:
