It turns out that there are nine dragons in the body of the warrior, which means that the warrior has a "strand of soul remnant" from the immortal. This means that he knows how to fight the immortal, even if he doesn't know how to do it himself. This is why he's so confident in his abilities: he knows that the immortal is too powerful to be defeated by him. He knows that he can't defeat the immortal by himself, so he'll have to fight in hand-to-hand combat. He realizes that if he had fought with the immortal "fair and square," he wouldn't have a chance.