The Bomb King is a special enemy in Final Fantasy X, created in the Species Conquest at the Monster Arena when at least five of each Bomb-type fiend has been captured. The cost to fight the Bomb King is 8,000 gil.
Bomb King uses Grow after every third attack; however, he does not Self-Destruct as is common for this species. Each stage of growth is accompanied by a change in attack.
At the start of the battle, the Bomb King Bashes one party member for moderate physical damage. After the first growth, he uses Fira; after the second, Firaga; and when he has peaked, he begins to cast Ultima. Counterattacks do not cause Bomb King to grow.
It is immune to the Gravity ability.
The best option widely is using the Celestial Weapons for defeating him.
A good strategy is to equip party members with Magic Counter weapons and Fire Eater armor. Once the Bomb King has grown once and begun casting Fira, his attacks will heal party members, but their counterattacks will not cause the King to grow. Using Haste on the Bomb King will speed up the battle using this strategy.