Jacob was shocked to see the legendary wyvern at its full glory. The last Wyvern he had killed in the Dark Ruins of the Rare Plains Trial was sleeping, and according to Immortika, it was an infant at extraordinary rank!
But this Wyvern seemed to be very close to achieving adulthood. A Wyvern has four growth stages: Infant, childhood, adolescence, and adulthood. It was born extraordinary, became epic in childhood, reached unique in adolescence, and Fable Legendary in adulthood!
Moreover, it was the true descend of the Mythical Dragon!
Furthermore, Jacob had never expected that an adolescent Wyvern could also take humanoid form. Not only that, but it could learn martial arts and possess terrifying abilities.
Now Jacob finally understood why he thought that this Flame Calamity wasn't a giant and its special features were so different from a traditional giant. It revealed its true form only when he was about to kill Flame Calamity.