If you wanted to get ahold of the most important book of magic in the Middle Ages — I mean, inspire-the-most-fantasy-Buffy-the-Vampiresque sorts of spells magic, replete with demons, charms, incantations, arcane use of astrology, etc., then you would have to look no further than the _Picatrix_.
It sounds like the name of a Pokemon, but Picatrix got its name from the Latin translation of an Arabic magical text — the former came from the mid-13th century, but the original Arabic was probably written a couple hundred years earlier. Most of the book is astrological magic, so to understand the spells you needed to understand the phases of the moon, the way the planets appear on the celestial sphere, and how to coordinate knowledge of which heavenly bodies were in various places in relationship to each other. All of this was elite knowledge, and probably made readers who could understand it feel specialer.
Here you see an illustration of an anthropomorphisized planet Venus. The various spells often gave instructions with vague directions — for instance, the amounts of spell ingredients aren’t specified. Hiding one’s insights to keep the information secret gets at the very definition of “occult” (from a root that means to darken or hide, like occlude), and is antithetical to the scientific method but par-for-the-course with Medieval astrology and alchemy.
Out of the 400 pages of spells, two gems stand out: in book three of the Latin version, there is a spell to create hate: you tell me whether you would feel hate if someone fed you this potion: “take 4 ounces of black cat’s brains. Grind them up, and mix them with an equal amount of dried and ground human excrement. Give it as food to whomever you wish. To be sure, that individual will hate”. Ha!.
In book 4, there is an oddly specific spell for avoiding hail: “when hail appears, if a menstruating woman throws herself onto the ground completely naked, raising her legs toward the cloud, the hail will not fall around her on that field or harvest”. It’s practically a Monty Python sketch already.
Source(s): For the _Picatrix_ generally and the spells specifically (pp. 201 and 264, respectively), see _Picateix: a Medieval Treatise on Astral Magic_, trans and intro by Dan Attrell and David Porreca, Penn State Press, 2019. Image, Biblioteka Jafiellonska MS 793, f 191v.