Okay. I'll give it another shot.

Sephiroth.

He is alot like Kain, when it comes to fighting. He is powerful in close-range combat with the Massamune and at a distance, with magic attacks like Shadow Flare. Then, there is the business of which form he takes on. In human form, he has greater mobility, being able to teleport and fly. In Bizzarro Sephiroth form, he has the ability to revive parts of himself after they are damaged and cannot be used any more. Safer Sephiroth is the most powerful of them all, and since Seph can take on all the magics used in his other forms, Safer Sephiroth's magic power plus the addition of his other magics, makes him quite formiddable.

Plus, he has no weaknesses. (Besides his storyline)

Go ahead. Destroy him.