One of my favourite writers of horror stories is the early 20th century author William Hope Hodgson, and amongst his works is a book of short stories entitled "Carnacki the Ghost Finder", which features the title character’s investigations into the supernatural and mysterious.
Carnacki frequently refers to a tome called "the Sigisand Manuscript", and even quotes from its ancient wisdom on the "ab-human". It is Carnacki's tenet that beyond the human sphere are realms of utter horror ever waiting to find channels into our own world. Of these one of the most terrible is the Saaaiti Manifestation.
Hodgson can be thanked for all those hours that Monster Hunters have spent cowering inside pentagrams whilst something awful tests their arcane defences. But the reason the Saaaiti Manifestation is particularly dangerous is that it incarnates in our world through some type of matter. The Club has fought Saaaiti manifestations of wood, cloth, electricity, blood, and even faeces. Every single time it has been a bugger to destroy.
When the Saaaiti manifestation is of a substance which actually forms part of a diagram of arcane defence - wood, or chalk, or something organic inside the circle, then it can ignore those defences entirely and simply go for the kill - or the soul leach.
As Carnacki puts it in his nastiest case, "The Hog": "I knelt down quickly and felt the floor with the palm of my hand, but it was quite normal to the feel, and that reassured me that there was no Saaaiti mischief abroad; for that is a form of danger which can involve, and make use of, the very material of the "defence" itself. It can materialise out of anything but fire."
However, in this instance Carnacki was wrong: "I found unmistakeable signs that it had indeed been a Saaaiti manifestation, for there had been no psychic or physical illusion of the melting of the violet circle [the arcane defence]. There remained nothing but a ring of patches of melted glass. The gutta base had been fused entirely, but the floor and everything was intact. You see, the Saaitii forms can often attack and destroy, or even make use of, the very defensive material used against them."
"Stepping over the outer circle and looking closely at the indigo circle I saw that it was melted clean through in several places. Another fraction of time and the Hog would have been free to expand in an invisible mist of horror and destruction into the atmosphere of the world."
As for the spelling, well within the book itself it is variously spelled Saaaiti and Saaitii, so my advice is please yourself.
IW