First seen in Day 162.
The boss monster of the 【Vesper Cave】 is the 【High Octorp】.
It's a monster that's similar to a chimera made of aquatic creatures, giving it a very grotesque appearance.
It's a humanoid that's approximately four meters tall, with its whole body covered in a dark red shell made of a material similar to chitin. On its abdomen is a huge circular mouth with a shape similar to a large drum, which had three rows of sharp fangs that moved subtly as it searches for prey. Its left forearm had expanded, transforming the four strange claws of its hand so they could be used as a shield, while its right hand is a huge claw similar to that of a Red King Crab. The lower half of its body is shaped like an octopus and it has approximately ten wriggling jellyfish-like tentacles growing out of its back. Its head was similar to a shark's in some respects, with four large eyes that were strangely similar to a deep-sea fish's, which were restlessly surveying its entire surroundings. It spoke the human language in a strange voice that you couldn't bear to listen to, which was emitted from the part of its body that was similar to a mouth.
Despite its weird and unpleasant appearance, it has the considerable strength you would expect of a boss monster.
Naturally, its octopus legs and right claw have supernatural strength. Its mouth-like part contains a strong, red dissolving fluid and the octopus ink that it releases can cause several negative status effects, including 【Blindness】, 【Confusion】 and 【Petrification】 among others. Its tentacles are the most troublesome of them all, though.
A powerful paralytic poison is secreted from the jellyfish-like tentacles on its back. Most people are immediately incapacitated from one sting of its tentacles. After that, they are either crushed by its eight octopus legs or finely chopped up by its claw, before finally being eaten by its abdomen's large mouth. This is the standard pattern it uses to kill adventurers.
In addition, it can manipulate the surrounding water, making it necessary to work out countermeasures before challenging it. By the way, it makes its appearance either by jumping out from within the rimstone pool or falling from a hole in the center of the ceiling. It seems to vary from time to time. It takes 10 minutes for the boss to respawn, and it drops [Ancient] class items: 【Vesper's Outer Shell: Octorp】, and【Vesper's Strange Blade: Octorp】.