Prelati's Spellbook

Prelati's Spellbook is a demonic guidebook with a cover made of glistening and wet human skin. It allows the summoning of an army of water demons from the depth of the seas of another dimension, High Thaumaturgy, and Greater Rituals. Rather than simply functioning as tome of spells and curses, the book itself functions as a prana core completely independent of its wielder's prana. Depending on the verses used, this allows for the usage of a class of ritual magecraft that tens of magi couldn't accomplish together. If the Spellbook itself is damaged, it is capable of regenerating. The concept comes from the R'lyeh text from the myth of Cthulhu, and François Prélati, a of friend Gilles de Rais known as an adept of black magic.

The water demons, without a discernible torso nor appendages, are best described as masses of tentacles with circular mouth-like openings marked with shark-like blades. Their innards spew a mist-like gas that would cause lung corrosion in a normal human. They are summoned by using the blood and flesh of creatures, living or deceased, as a sacrifice, and they must constantly receive prana from the Spellbook. They will stay summoned as long as they receive prana, allowing Caster to leave them as guards to his workshop while he is away. No matter how many are destroyed in close combat, their numbers will never decrease, as the flesh of the defeated demons will instantly spawn new ones to take their place. If the connection is severed for even a moment, they will all instantly dissipate into the blood of the original sacrifices. If Caster is in need of an escape route, he can surge prana from the Spellbook into the blood in order to cause it to boil and evaporate into a bloody mist.

Caster also has the ability to become absorbed with the Spellbook into a mass of demons, which slowly fuse together into a masive single demon, of which all of the summoned familiars had been bits and pieces, the size of a building. With a similar structure to an amoeba, it has no bones or organs and it feels no pain, even with a third of its body blown away. It continuously regenerates, no how much damage is done, allowing it to survive an assault from four different Servants at once without any permanent damage. It has tentacles capable of swatting an F15 fighter jet out of the sky with ease, and after it crashes into the demon's body, the F15 is swallowed by it without leaving a trace. In order for it to be destroyed, either Caster's master must be killed, allowing Caster to naturally fade away after his prana supply is used up, or an Anti-Fortress attack, such as Excalibur, must be used in order to eradicate the entirety of its flesh and kill Caster deep inside the heart of the creature.