The boss-koala

Hugo didn't wait for the boss-koala to approach. He just cast the Cloak of Thanatos spell and bolted away like lightning. Within no time, he was nowhere close to the banks of the underground stream.

He tempered his curiosity about the appearance of the boss-koala by reminding himself that he was definitely not a tourist on a sightseeing trip at a zoo back on Earth.

Freya had warned him that the approaching calamity beast was most likely a Grade-S. 

Grade-S calamity beasts, which were referred to as rank-4 occasionally, had mystic capabilities that rivaled those of a mystic knight. That meant their abilities were two complete rungs above Hugo's meager scholar realm powers.

Advancing to the mystic wizard realm required opening all the mana channels in one's body and connecting with the earth-star chakra.