In Call of Cthulhu (CoC) 7th Edition, Magic is pretty straight forward, especially with the Summary of Magic Rules on page 419 Keeper Rulebook. But some rules are hidden in the text or are confusing due to wording.
Q: Do you tell the Players how many Magic Points (MP) are required for a spell?
A: No, not initially. But in the spell ritual, there will probably be hints as to how much it might be. An example would be "Ye Spell may cause tiredness and if caster is unhealthy, a nose bleed." or "Ritual Circle participants may faint and in extreme cases die depending on how many hours of chanting and dancing continues." For minor spells, after a successful casting, I would tell the Player how much it would cost. For major rituals used to mainly banish a major Big Bad Guy, I would ask each Player to write down how many MPs they are spending and hand it to me in secret. Then I would add it up and see if they reach the required amount of spend. Remember, you can spend all your MP and overspend, by spending HP in addition to MP. When you overspend, I would describe the physical effects of the HP spend such as a nose bleed, dehydration, burst blood vessels, shriveling like a raisin, or even death by turning into dust. If the ritual is long (over several hours), I may allow additional MP / HP spends to complete the ritual. e.g. their first group spend wasn't enough. I would hint that something might be happening, but maybe the spell is failing and ask them if they want to spend more.
Q: When PCs find a tome and inside it is a spell and they decide to cast it. How much about the spell do they know and what does it do? Do they cast it to find out what it does? How vague or specific are you about what the spell does?
A: It depends on how thorough the tome is and if the PC skimmed the tome (Initial Reading) vs Full Reading. If you did a full reading and it's not a fragment of a tome, you'd think the spell is in there with some context. So, there are enough clues to figure out what the spell does. "Bringing a corpse back to life" might mean: zombie, reanimation, resurrection, possession by evil spirit (a la Evil Dead). Who knows? Undesired side-effects? Possibly. If it's an old tome with notes in the margin, there might be additional clues as to what the spell does and possible side-effects.
But if it's a fragmentary manuscript and a skimmed reading and a "go for it" casting of the spell, then the results could be even worse. It'll be a GM potluck.
Q: A Tome takes 20 weeks to read, but there's no time in the scenario to that, so what's the use of the book?
A: You can skim the book (Initial Reading). So, you're basically flipping through the book and reading various chapter headings and maybe the first paragraph of each chapter. Also noting if there are diagrams (most likely spells). Then going back and deciphering the potential spells. (p.176 & p.419 Keeper Rulebook, "Learning a spell from a Mythos book.") This requires typically 2d6 weeks (or shorter depending on the scenario's needs) and an optional Hard INT roll (also depends on the scenario's needs).
Q: Why would I Push the initial casting of a spell?
A: If you fail your initial casting of a spell, you can either Push the casting or relearn the spell. Relearning the spell requires pouring over the ritual trying to make head and tails of it and figuring out what you did wrong (taking on avg 2 weeks, p.176 Keeper Rulebook, Learning a Spell from a Mythos Book.) In emergency situations, you may not have the luxury of doing that and you would want to Push the spell. The consequences of failing a Pushed Casting Roll may not be too bad. See p.178 Keeper Rulebook, Failing a Pushed Casting Roll.
A: If you fail your initial casting of a spell, you can either Push the casting or relearn the spell. Relearning the spell requires pouring over the ritual trying to make head and tails of it and figuring out what you did wrong (taking on avg 2 weeks, p.176 Keeper Rulebook, Learning a Spell from a Mythos Book.) In emergency situations, you may not have the luxury of doing that and you would want to Push the spell. The consequences of failing a Pushed Casting Roll may not be too bad. See p.178 Keeper Rulebook, Failing a Pushed Casting Roll.
Q: Learning how to cast a spell is really hard. What if we really want to succeed in casting it?
A: Once you've successfully cast a spell, you can cast it later without having to make any rolls, other than any spell targeting requirements (p.177-178 Keeper Rulebook, Casting Spells.) So, if there is time, it would benefit the PCs if they learn the spell beforehand and do a successful casting in a non-stress situation first.
Or if push comes to shove, you can Push the casting and immediately try again, but the consequences could be terrible. See p.178 Keeper Rulebook, Failing a Pushed Casting Roll.
Q: Does POW regenerate?
A: POW does not regenerate, but there are 2 ways to gain it:
A: POW does not regenerate, but there are 2 ways to gain it:
1. When you roll 01 on a Luck roll, roll % and if above POW, gain 1d10 in POW(p.179 Keeper Rulebook, How Sorcerers Get That Way.)
2. After casting a spell requiring a POW vs POW contest and winning it, roll % and if above POW, gain 1d10 in POW (p.419 Keeper Rulebook, Increasing POW or p.179 Keeper Rulebook, How Sorcerers Get That Way.)
Q: In Tomes of Eldritch Lore, under Cthulhu Mythos, what are the +A/+B percentiles?
A: Cthulhu Mythos: +Initial Reading % / +Full Reading %
Cthulhu Mythos: CMI / CMF
Q: If your Cthulhu Mythos skill is greater than any Tome's Mythos Rating, does it mean you can't get any Mythos skill out of it?
A: Even if your Cthulhu Mythos is above a book's Mythos Rating, you still gain Cthulhu Mythos out of it, but it'll be the CMI value. See p.174 (bottom) - 175 (top) Keeper Rulebook. You can always reread a Mythos Tome, but remember the time to read doubles each time you do so.
Q: Can I use a Mythos Tome as reference material?
A: Yes. The Mythos Rating is the percent chance that a Tome contains useful specific information, but this requires a full study beforehand. And you must keep track of what was looked up before for consistency's sake. See p.175 Keeper Rulebook, Mythos Rating -- Books as References.
This also explains why Cultists and Wizards have a library of occult books and why they continually study and reference them.
In my longer campaigns, such as Masks or HotOE, the PCs kept tomes they found in their luggage, so they can read them during long ocean voyages or to do research. I had a 3x5 card for each book, like an old fashion library checkout card, and kept track as to who read them, who's reading it, reading start date/end date, and what's in each book. This also keeps track as to who has done the Initial Reading and/or a Full Reading of that book. Also some PCs only had time to read a portion of a book before returning it, so this keeps track of how much of the book they've read if they plan on finishing it in the future.
Q (CB): An investigator has read, and is in possession of 4 Mythos tomes. They want to use the Mythos Rating to research that weird thing they saw. Each takes 1d4 hours. If they are willing to spend the time, do they get 4 attempts (at differing ratings of course)?
A (MH): I’d let each investigator take a different book and give it a try. Otherwise that one PC would be just researching while the other PCs are doing other stuff, pretty boring for that one Player.
But from the question, I assume only one PC has fully read all the books. In that case, I'd say it depends on how nice the GM is. Depends on which books and what they're looking up. For instance, if they're trying to find info about Deep Ones, well a book on the Andes or Tibet will have 0% chance of having info on Deep Ones. Also remember if they tried to look up specific info about the Mythos and it failed, that book contains no info about that topic, you should keep track as to what the book contains or doesn't contain.
Also the info found maybe as clear or obscure as the GM wants. i.e. some info, but not so much it breaks the scenario.
I may also claim that if your Cthulhu Mythos is above the book's Mythos Rating, you know more than the book and there's no point in using the book unless they want to Push and risk SAN loss.
A (RS): I'd streamline the process by giving one roll for the specific research across tomes. If the information is necessary for the investigators to have, give them the information no matter what, but make it take longer if they fail (automatically make each die roll four hours, or add more D4 hours to the time), or minimize the study time on an Extreme success.
Q: Can you dodge or fight back against a spell?
A: No, unless there's some combat component, such as touching your target.
Q (ED): For reading mythos tomes, does the sanity loss apply after an initial reading or after a full study?
Q (ED): For reading mythos tomes, does the sanity loss apply after an initial reading or after a full study?
A (MH): Both. You lose SAN both times and any additional times you read it. See p.419 Keeper Rulebook for summary of rules. Also note when it says Roll for Sanity loss, it means roll for the amount for San loss, not roll for a SAN save. SAN loss is automatic when reading tomes.
Q: During full study of a Mythos tome, if your Cthulhu Mythos is already greater than (or equal to) the tome's Mythos rating, do you gain CMI or CMF/2?
A: CMI. See p.175 Keeper Rulebook, Full Study. It explicitly states CMI.
But on p.419 Keeper Rulebook, Full study of tome, it states CMF/2. I think this is how CMI / CMF were initially created. On most, but not all tomes, CMI = CMF/2 (rounded down). See p.237-239 Keeper Rulebook, Table XI: Mythos Tomes.
For consistency and simplicity, I'd just use the pre-calculated CMI.
Q (JO): Can PCs "cheat" by recording a ritual chant on a Dictaphone and play it, so they're free to do other actions?
Q (JO): Can PCs "cheat" by recording a ritual chant on a Dictaphone and play it, so they're free to do other actions?
A (MH): Most rituals require intention and a spend of POW, MP, and/or SAN to complete. Without those components, it probably won't work. If the ritual doesn't require a spend of those things or if you, as GM, allow the recording, but the spend of points is channeled through the PCs anyway, then it might work.
If you do allow it, a wax cylinder has a very short play time (3 minutes max) and a creature can throw things or make the floor shake that can disrupt the Dictaphone player. So, PCs have traded one thing for another. Not a get out of jail free card. Also a Dictaphone has a lousy speaker (a horn) and isn’t very loud, so maybe it only works in a specific direction or to a limited extent. Or not at all. Also repeated play wears the wax cylinder down.
https://en.wikipedia.org/wiki/Phonograph
Q (ZE): How do you approach telling players about Mythos Tomes. When a player finds a tome, should the keeper tell them its statistics (Cthulhu Mythos Points gained, sanity loss, time of study) before they attempt to read it, or should this information be hidden until the players make an attempt at studying it?
Q (ZE): How do you approach telling players about Mythos Tomes. When a player finds a tome, should the keeper tell them its statistics (Cthulhu Mythos Points gained, sanity loss, time of study) before they attempt to read it, or should this information be hidden until the players make an attempt at studying it?
A (MH): I keep it hidden until they can reasonably figure it out.
That's what Initial Reading is for. Those books don't have blurbs on them. You gotta dive in the deep end to find out. I don't disclose the stats until they've taken the SAN loss and gotten their Cthulhu Mythos pts. I generally won't disclose the Full Reading pts either, but most of them are about double the Initial Reading Mythos pts.
For spells, I disclose whether there are spells in it after an Initial reading. I do expect spells to have diagrams and such, so even without an Initial reading, you can tell there are spells in them. You should also obfuscate the spell names. The Grand Grimoire has optional names. I also don't give out what the spells does, but give a general idea of what it might do (sometimes incorrectly or hide its possible side effects).
Q: How do you spot spells in Mythos Tomes?
A: There are always sigils to be drawn somewhere (on paper, on a surface, on a body part), hand movements and gestures, ingredients (herbs, incense, liquids, bodily fluids), or summoning circles and such. I assume these will be illustrated, much like secret Kung Fu manuals. If you see an illustration, it's probably a spell. There's probably a title, probably in an old tongue and slightly obscure. What the spell does is probably obscure too unless there's marginalia by someone who tried casting it before. If it's translated, it might be easier to figure out unless it was translated from a partial manuscript.
Q (GMD): If an investigator casts a spell and fails the first time. They then push the roll and fail again taking the increased cost of the spell, but the spell still casts with the added side effect that comes along with it.
Q (GMD): If an investigator casts a spell and fails the first time. They then push the roll and fail again taking the increased cost of the spell, but the spell still casts with the added side effect that comes along with it.
If the investigator wants to cast that spell again, do they do it regularly or do they have to go through the 'First time casting' process all over again?
A (MH): I'd say if they want to mis-cast it again, they won't need to roll, but they get the same side effect from the pushed roll. e.g. repeat the same mistakes they've done before. If they want to avoid the side effect, they'll need to relearn the spell and make another casting roll. See p.178 Keeper Rulebook, Failing a Pushed Casting Roll.
Q (TS): Does casting a spell that has a sanity cost of 1D6 cause temporary insanity on a roll of 5+? Also, does losing enough sanity through spell casting cause indefinite insanity?
A (MH): Yes and Yes. Mythos spells require understanding of Cthulhu Mythos Magic, so casting those spells pushes you to complete understanding. Some spells do not have a SAN cost. Some are considered Folk Magic, See p.13 the Grand Grimoire of Cthulhu Mythos Magic.
A (ENR): That's the cost of magic... and also why most villainous cultists are insane (0 Sanity).
Q (RH): Quick question on instantaneous spells. I know they are described in the book as working just like readied firearms, but my understanding is the readied firearm bonus applies for further rounds as long as said shooter is still shooting and isn’t doing anything fancy like running or obviously reloading.(i.e. it’s not just for the first shot).
Does that principle apply for instantaneous spells? In other words can a powerful sorcerer can keep the +50 Dex bonus if the caster keeps casting the instantaneous spells?
I assume if you wanted to switch from melee to an instantaneous spell you would need to do so on your usual turn order and cannot interrupt, in much the same way a player can’t just announce ”I’m pulling out my gun” in the middle of the round for a sudden +50 DEX.
A (MH): I think instantaneous spells are always ready. They’re just very quick to cast. You do not need to pull your spell gun out of your holster. See p.243 Keeper Rulebook, Casting Time and Spells in Combat.
You can only act once in each round. If you were fighting in combat and was acting at Dex in the initiative order, and wanted to cast a spell for the next round, you need to notify the GM that you are casting an instantaneous spell to go at Dex + 50 for the next round. If you changed your mind in the middle of combat before you acted, I'd leave that up to the GM to decide. Most likely you'd go in Dex order, you cannot suddenly cast a spell as an interrupt before the creature hits you, by claiming that a instantaneous spell goes at Dex + 50 and before the creature goes, this seems like cheating.
Another example, if you initially said you were going to cast an instantaneous spell and then changed your mind and decided to fight in combat, your initiative should drop down to Dex before you can act. e.g. you cannot fight at Dex + 50. I guess if your choice was to shoot a gun already in your hand or cast an instantaneous spell you can do either at Dex + 50. The only edge case is if the spell requires a hand gesture that uses your dominate hand, then you'd have to decide beforehand. And if you change your mind, you'll have to drop down to Dex before you can act because you'll either have to holster your gun or draw it before you can act. Most spells don't have this much detail, so it'll probably never come up in a game.
Q (U): Some spells have a Sanity Cost in the book. I think this is something that happens each time you cast the spell and is not a cost for learning it? If that's correct, then is there a Sanity save roll each time you cast the spell and you lose that much if you fail it? Or is it automatic.
Q (U): Some spells have a Sanity Cost in the book. I think this is something that happens each time you cast the spell and is not a cost for learning it? If that's correct, then is there a Sanity save roll each time you cast the spell and you lose that much if you fail it? Or is it automatic.
A (MH): You are correct, the Cost listed for the spell is for casting the spell, not for learning it.
Reading books and spell casting are voluntary, so the SAN loss is automatic. There is no Sanity save roll. Best way to check this is if you see something like 0/1d6 that is an indication there is a Sanity save roll and the resulting SAN loss for succeeding/failing the roll. If you only see 1d6, then there is no Sanity save roll, and the loss is automatic.
Q (TDK): I bought The Grand Grimoire of Cthulhu Mythos Magic from Chaosium, and it talks about the different phases of the Moon having the potential to enhance certain types of spells.
Q (M): Do spells that cause you to lose 5+ SAN points automatically drive you crazy and in addition to not being able to be cast, they had better not even publish them?
A (MH): Spells that cost you SAN will eventually drive your SAN to zero and thus permanently insane. Once you've successfully cast a spell, you can always cast it in the future at 100% chance success. If a spell costs 5+ points SAN, have the PC roll the INT roll after the spell goes off to see if they go temporary insane (p.178 Keeper Rulebook, see sidebar example). Also once your SAN goes to 0, you basically have infinite negative SAN. Insane cultists (0 SAN) can cast spells without SAN cost. (p.177 Keeper Rulebook, Casting Spells, Having no Sanity points does not prohibit spells from being cast—if it did, there would be no cultists.)
Why would someone rational write these spells down? Well, maybe they wrote it down during a bout of madness? Or a mad cultist wrote it down because their god told them to. Or the spell worked and it's worth using in an emergency to save the world -- again.
You have to remember that in CoC, Insanity is not your DSM definition or causes. Insanity is understanding Cthulhu Mythos hyper-reality and hyper-geometry. Cultists have 0 SAN because They Understand the Unknown and Unknowable.
Q (TDK): I bought The Grand Grimoire of Cthulhu Mythos Magic from Chaosium, and it talks about the different phases of the Moon having the potential to enhance certain types of spells.
Could someone tell me how they handle lunar calendars or Moon phases in their games? I'm tempted to use that idea, but it seems too complicated for me.
A (MH): I use this website: https://www.timeanddate.com/calendar/?country=1&year=1923
If PCs ask what phase of the moon is in, I look it up. As most rituals happen either at New or Full Moon, I use that as a ticking clock for the PCs if they bring this up.
Other Q&A:
