Sciomancy

Meaning: Cotgrave:

Divination by conference with the shadows of dead men. 

Usefulness: 2 (There's possibly a case to be made that reading authors long gone is 'conference with the shadows of dead men'.  Otherwise this word is probably only useful if you're writing a horror story, or reviewing The Sixth Sense.)

Logofascination: 2 (A specific form of necromancy, etymologically from the Greek for shade and shadows.  There's some suggestion that it can also mean divination by shadow - what shape yours casts, or the movement of shadows. I haven't found much to corroborate either way - what information I could find regarding sciomancy refers back to Rabelais, and I had no particular desire to go digging in the dark corners of the internet for the details of necromancy.)

In the wild: No; see comment above.

Degrees: 1

Connections: n/a

Which is used in: G&P, Book the Third, XXV: In which Panurge consulteth Herr Trippa. This is the last -mancy mentioned in the chapter, twenty-fourth post on the topic and 150th SDOSTU post overall.  There are still a few -mancys left, though, as I skipped a few of the more general or better known ones, and will be circling back to wrap them up. In the meantime, Herr Trippa offers:

Or yet by the mystery of necromancy? I will, if you please, suddenly set up again and revive someone lately deceased, as Apollonius of Tyane did to Achilles, and the Pythoness in the presence of Saul; which body, so raised up and requickened, will tell us the sum of all you shall require of him: no more nor less than, at the invocation of Erictho, a certain defunct person foretold to Pompey the whole progress and issue of the fatal battle fought in the Pharsalian fields. Or, if you be afraid of the dead, as commonly all cuckolds are, I will make use of the faculty of sciomancy.

Sciomancy is presumably less scary because it is the ghost, rather than the resurrected body. I'm not sure why cuckolds are particularly scared of the dead, unless there's a general association with cowardice.