Crystal Cave was not something particularly unfamiliar to the adventurers and that was what had been created for Portal 5. With monsters all merged and infected by the constant exposure of mana had made them into living crystal monsters. Only some were alive as infused crystal monsters.
Or that was the premise most adventurers had thought mainly because most crystal caves they had encountered were of that kind of nature. This usually meant they were of rank C and above. But right now, this was a Rank E- portal so most of the monsters the adventurers encountered were monsters that had just been infused by the crystals.