Over 550 spells of dire consequences, secrets, and unfathomable power Here are gathered spells drawn from over thirty years of Call of Cthulhu supplements and scenarios. Each spell has been revised for the Call of Cthulhu 7th edition game, including optional Deeper Magic for the most powerful of Mythos sorcerers and monsters, with which to beguile and confound investigators. Packed full of advice and guidance on diverse matters including spell names, elements of spell casting, magical components, and astronomical considerations. Plus flawed spells, ley lines, folk magic, and the magic of the Dreamlands. Use this grimoire as a resource, a play aid, and as inspiration when designing scenarios. The Grand Grimoire of Cthulhu Mythos Magic is an essential supplement for Keepers of Arcane Lore. Magic in Call of Cthulhu is not your run-of-the-mill epic fantasy magic. It is not a tool; it is reality, with great and usually irreversible consequences on the minds of the hapless men and women who are stupid enough to use it. The book starts by discussing magic's principles, as well as star alignment. As an example, divination, prophecy and communication spells will work better on Wednesdays, and even more so if it is a New moon.Casting a spell is not a scientific experiment which, all things considered, will always produce the same results.Spells leave magical residue, usually an unwanted event outside of the spell's effect. Too much spellcasting in the same place however can stretch the boundaries of reality, potentially filling these places with magical powers, enhancing future spells or calling forth creatures from beyond