Cap 671: Why is it so hard to kill!?

Pov Queen Melissa: 

This colossal monster that had a body similar to that of a fat giant, but had thick spider legs made of bones, in addition, it had four arms that had silver claws like metal, it had no head, but it had 2 large eyes on its chest and a large vertical mouth that runs from the top of the chest to the bottom of the belly, it also had six tentacles the thickness of a tree on its back. 

I tried to rip off one of the tentacles but the other one grew too fast, I use my attacks but nothing seems to have any effect on it. 

"< Weapon Summon: Demon Guardian's Staff >" (I) 

I wave my hand forward gathering my mana and demonic energy to summon a weapon that I have a contract with, with this staff, I will lack less of my energy, my attack power doubles, and my demonic spells become easier to control. 

"< Drain Vitality >" (I)