Destroyed Behemoth

The Destroyed Behemoth (デストロイドベヒーモス) is a black, yellow, and red Behemoth, with a flame design on its body. Exclusive to Kingdom Hearts Final Mix, it replaces the Behemoth that is fought during the 40th seed of the Hades Cup in the first Kingdom Hearts, and is treated as a new Heartless, earning itself an entry in Jiminy's Journal.

Kingdom Hearts Final Mix
Just as the original Behemoth, its weakness is its horn, and it is immune to all elemental spells. To take it down, cast Aeroga on yourself, get on its back, and attack the horn incessantly!

If you cannot evade the bolts of lightning by using Dodge Roll on time, keep having Aeroga on. This can at least reduce the damage. Rather than using Ethers or MP-restoring items, make use of the MP generated with every hit inflicted on the Destroyed Behemoth.