Despite already reading about them and knowing that Dust Snakes were among the apex predators of the Great Desert, Rex was still shocked by what he saw. King was indeed a King among the apex predators.
Every single one of it's 6 skills were a situation changer. Alone, they were good enough to be the special trump cards of other beasts.
But to King, they were its normal everyday skills.
Unlike most beasts, King didn't really have a trump card skill. Its trump cards were its 4 mystic affinities which was the main reason which made it so OP in the first place, and its special poison organ and special ability.
With all these placed in one beast, King became the strongest and most all-rounded of all Rex's companions. In a fair battle, King was even stronger than himself currently.
With his mystic sword domain, his vampire abilities, and his other powers, the fact that King could still beat him spoke volumes about the capabilities of his newly created transformed beast.