The spells of the Cthulhu Mythos consist of hyper-geometric equations that when properly cast, cause a specified effect. The magic labelled "Mythos" (sometimes called Hyper-geometry) is the easiest magic to learn. It is also the most costly. The power of the Mythos involves forcing the mind to encompass alien/extra-dimensional physics to produce an effect in this world.

Learning and Casting Spells

To learn a Mythos spell, you must have a Mythos Lore equal to the Complexity of the spell. The cost to learn a given spell is Complexity x2. (Of course, you must also have access to the spell.) Contact, Call/Dismiss, Contact Deity, Summon/Bind, and Enchantment spells may be cast from a book without being learned.

Most Mythos spells require components (Verbal, Somatic, Material, and/or Ritual) as foci. A spell with no components may be cast with no visible sign.

Most Mythos spells have a point cost. While Greater Beings and Great Old Ones may have additional pools usable for this, most lesser beings are limited to their Willpower, making many Mythos spells nigh-impossible to cast.

Mythos magic erodes the user's sanity. If a caster does not have a Morality Path, the next most likely target is used to determine Sanity loss. There is ALWAYS a loss when any earthly being employs this magic, no matter how powerful or depraved. Alien beings MAY be able to avoid these losses at the GM’s discretion. Nearly any being may use Mythos magic with the proper training.

Most effects that would resist magic work normally against Mythos Magic.

Casting Time

Casting Time is typically specified in the spell description. If not specified, it is 1 turn. This may be shortened by the Fast Casting background, but can never be reduced below one turn.

Spellcasting is always a committed action; while casting a spell, you cannot split your action or take any other action.

Mythos tomes

Spells cannot be learned from Mythos tomes until the book has been studied and fully understood. Mythos spells are virtually never written out clearly. The authors are almost always insane or inhuman; their methods and motivations are inscrutable, perhaps even to themselves. Spells must be puzzled out from hints and innuendo over weeks or months of study. It is sometimes necessary to learn certain spells before others in a particular tome (in essence, deriving one spell first, followed by a related one).

Learning a spell does not tell you what it does or how it works; you have only learned the steps to cast it. To learn more, you must cast the spell …

Truly significant tomes such as Liber Ivonis and the Necronomicon might raise the character's Library rating. Such tomes are freakishly rare, so the pedigree of each copy must be established.

Mythos Tomes as Gifts

Mythos tomes may be awarded as Gifts. In general, a Gift will consist of a single tome, though it may include more than one tome if the tomes involved are particularly weak. The most powerful tomes will never be awarded as Gifts.

A typical minor tome will contain 4 to 6 spells. Such a tome is a suitable Gift by itself.

The High Roller requesting the Gift generally cannot select either the tome or the spells. A character who knows of a particular minor tome and requests it by name might receive it if it is deemed suitable. A character who makes a presumptuous request may receive nothing more than a hint to the location of the requested tome – the more powerful the tome, the vaguer the hint. This hint will be the entire Gift. The tome in question will almost certainly be in the possession of a powerful caster or organization; obtaining it will require a very difficult Side Game, or series of Side Games.

It is never possible to request a particular spell or a tome which includes a particular spell.

Inscribing Spells

Writing out a spell requires triple the number of successes required for the spell's Sanity check, or requires a Sanity check at Difficulty 7 if the spell did not have one.

Spell Research

Researching a spell requires an extended Mythos Lore skill check at Difficulty 8. A Conviction check may be required with each research roll, and if casting the spell requires one then each research roll will definitely require one (at the same Difficulty as for casting the spell).

Each research roll requires one Downtime. A botched research roll results in the loss of all accumulated successes. You cannot receive Study Points or teach or be taught by another character in any Downtime in which you conduct research.

Success requires a certain number of successes, generally at least 10 times complexity, and sometimes more. Of course, a line of research may prove to be a dead end, or may lead in a completely unexpected direction.

If you spend your Downtime in research, you begin the Game at half Willpower, as you spend Willpower on a daily basis in the course of your research.

Players conducting spell research must detail the approach they are taking and roleplay as appropriate. A Side Game may be necessary.

Mythos spells are generally dangerous and unstable, and are usually malign. Researching a safe or benevolent spell is seldom possible. It is generally impractical to improve or make minor modifications to an existing spell; it is much easier to create a completely new spell, though the basic principles involved must be known (usually from learning and gaining understanding of a spell that uses the same principles). It is possible to combine elements of separate spells, though the combined spell will be more difficult than the originals. The whole is greater than the sum of the parts …

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