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. It has the same model as the Bomb.
Bomb King uses Grow after every third attack, but he does not Self-Destruct. Each stage of growth is accompanied by a change in attack. Unlike other Bombs, he grows thrice rather than twice.
At the start of the battle, 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.
Celestial Weapons are good 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.