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Impossible Arithmetic

3rd-level divination (ritual)

Casting Time: 1 action

Range: Self

Components: V, S, M (an offering to the Great Old Ones, which the spell consumes; see text)

Duration: Instantaneous

You gain a glimpse of a terrible truth, receiving one truthful answer regarding the Mythos. The material component is an offering to the Great Old Ones. It is up to the GM to decide if the offering is acceptable. Rarer or more obscure information requires more exotic offerings: for example, a silver holy symbol of a Great Old One would be appropriate to learn a vague clue about the components required to cast a minor formula or to learn one fact about a minor Mythos monster. A spell scroll of an uncommon spell of 2nd level would be suitable to learn about the goals, methods, or origins of a challenge rating 5 to 10 creature.

A rare wand or one or more alchemical curiosities worth at least 1,000 gp would be suitable to learn about a challenge rating 11 monster or understand how to perform a formula without detailed instructions. An especially impressive rare magic item or occult art object worth 5,000 gp would be a suitable offering to learn the likely weaknesses of a challenge rating 17 monster or deduce what Great Old One a secretive cult is about to awaken based on vague clues, as well as some vague hints about how to stop them.

Section 15: Copyright Notice

Sandy Petersen’s Cthulhu Mythos, © 2018, Petersen Games; Authors: Sandy Petersen, David N. Ross, James Jacobs, Arthur Petersen, Ian Starcher.