The Nargacuga that the man in black was riding was a sub-dragon. Although there was a big difference real giant dragons and sub-dragons, they were still an astounding creature to ride. The hunters rode nothing but ordinary steeds, which weren't even worth mentioning compared to sub-dragons.
Although the so-called sub-dragon was essentially only a beast, it was a beast transformed by giant dragons using their own blood as a catalyst. Thus it had nearly reached the peak capacity of a beast because its blood had been optimized from years of repeated experiments. As long as it had sufficient food and time, every one of them could eventually become a devil monster.
