Mordenkainen's Lost Notebook

Genius Loci

9-level Abjuration

Choose a location no smaller than 10 by 10 feet and no larger than 100 by 100 feet within range. The spell grants the location a permanent guardian. As part of casting the spell, you must task the guardian with a specific purpose, and that purpose must in some manner involve protecting the location to which it is attached. The task can be very general, such as “Slay any creature who comes through that door,” or far more specific, such as “Kill any elf who tries to take the black sword from the sarcophagus.” The task can’t mention the names of individual creatures or require unseen knowledge such as alignments, allegiances, or true names. Finally, the task must be simple enough to clearly convey in one or two sentences. If the triggering event occurs, the genius loci manifests in the location you specified when you cast the spell, taking the form of an elemental (MM, p124). When you cast the spell, choose air, earth, fire, or water. When the guardian manifests it immediately attempts to carry out the task you specified. Once the casting is complete, you have no control over the spirit’s actions. If you trigger the manifestation, it attacks you just as it would any other creature which triggered it. The elemental behaves in all ways as a normal elemental of its kind, within the parameters of the task you assigned it. If the manifested spirit’s form is slain, it can’t manifest again for 24 hours after being “destroyed.” Importantly, the spell is not broken. The only way to permanently break a genius loci spell is to permanently defeat the guardian spirit’s purpose. If, for instance, the spirit was commanded to “Prevent the Book of Magius from being destroyed,” the destruction of that item renders the guardian’s existence moot. When not actively involved in protecting its territory or following its task, the spirit shows no sign it exists. When it manifests, the creature springs into being out   of nowhere. Anyone viewing the area with detect magic or a similar effect sees an overwhelmingly powerful aura of conjuration magic. True seeing reveals the spirit wandering its territory, appearing as a vague, hazy silhouette.