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Piero S. P.
Italy
Turin
"If our gods and our hopes are nothing but scientific phenomena, then it must be said that our love is scientific as well." - L'Eve Future
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Has anyone got the odds for chaos manifestations with Magic dice?
Is there an alternative push-your-luck magic system for WFRP2ed? 
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Robb Minneman
United States
Tacoma
Washington
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No, but I'll run through the math of how to calculate them.
It's actually often easier to think in terms of not getting Tzeentch's Curse than it is to think in terms of hitting it. If you're rolling two dice, then your chance of not hitting Tzeentch's Curse is nine-in-ten. The first die roll comes as it is, and then the second die roll has a nine-in-ten chance of hitting it. So your odds of a chaos manifestation on two dice is 1/10, or 10%.
It gets a little more complicated with three dice. Again,the first die comes out as any number from 1-10. Then your second die has a 9/10 chance of matching. And then the third die has an 8/10 chance of matching the second. So your odds of not getting a chaos manifestation are 8/10*9/10=72/100. 1-72/100=28/100, so the chance of hitting Tzeentch's Curse is 28% with three dice.
Most of those are still minor manifestations. Your chance of getting a major chaos manifestation is only 10/1000, or 1%. The math: first roll comes as is. Then the second and third rolls must match that number. That's 1/10 each, so your odds are: 10/10*1/10*1/10, or 10/1000=1%.
I'll leave the odds on four dice as an exercise for the reader.
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Piero S. P.
Italy
Turin
"If our gods and our hopes are nothing but scientific phenomena, then it must be said that our love is scientific as well." - L'Eve Future
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robbbbbb wrote: No, but I'll run through the math of how to calculate them.
It's actually often easier to think in terms of not getting Tzeentch's Curse than it is to think in terms of hitting it. If you're rolling two dice, then your chance of not hitting Tzeentch's Curse is nine-in-ten. The first die roll comes as it is, and then the second die roll has a nine-in-ten chance of hitting it. So your odds of a chaos manifestation on two dice is 1/10, or 10%.
It gets a little more complicated with three dice. Again,the first die comes out as any number from 1-10. Then your second die has a 9/10 chance of matching. And then the third die has an 8/10 chance of matching the second. So your odds of not getting a chaos manifestation are 8/10*9/10=72/100. 1-72/100=28/100, so the chance of hitting Tzeentch's Curse is 28% with three dice.
Most of those are still minor manifestations. Your chance of getting a major chaos manifestation is only 10/1000, or 1%. The math: first roll comes as is. Then the second and third rolls must match that number. That's 1/10 each, so your odds are: 10/10*1/10*1/10, or 10/1000=1%.
I'll leave the odds on four dice as an exercise for the reader.
Thanks Rob, I've incidentally stumbled upon your variance discussion in wargames, just today. 
So throwing 3 dice makes for a significant risk. Roughly one in every 4 spells should activate a minor chaos manifestation. While, if my exercise is correct, with 4 dice this increases roughly to 50%.
Hum. I'm thinking. Since I've put a rule in our game that forbids the re-roll of magic dice (as in my opinion would make the Curse impossible), in fact we are well into the Bogenhaffen adventure and we had the Mistaken Identity -> Bounty hunter mini adventure -> Grapes of Wrath -> Stormy Marriage mini adventure -> Shadows over Bogenhaffen. And still no Curse has ever been triggered. It is true that my player really uses magic very sparingly to avoid it...
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Robb Minneman
United States
Tacoma
Washington
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You've run the math properly on four dice.
Not allowing re-rolls on the magic dice doesn't make Tzeentch's curse impossible, but it does make it less likely to occur. On two dice, for instance, you're likely only to re-roll when you get doubles. You pick up one die and re-roll, and your chance of hitting the same number again is 1/10. So your chance of getting a Chaos manifestation drops from 1/10 to 1/100.
On three and four (especially!) dice, that gets to be a little more complicated. On three dice, you're basically reducing your chance of a major Chaos manifestation from 1/100 to 1/1000 (using the same math as above; of course you're still forced to take a minor manifestation at that point.) Where it really helps is in reducing your chance of a minor manifestation. If you've got a minor manifestation you've got two of one number and one of another. You re-roll one of the doubles and have an 8/10 chance of not matching an existing die. So you drop your chance of a minor Chaos manifestation from 27% (28%, minus 1% for the major manifestations) to 2/10*27%=5.4%. (And then you still have the odds of what happens on a major manifestation.)
Four dice is, again, a lot more complicated than either of the cases above. Suffice it to say that without a re-roll, throwing four dice is immensely dangerous and should only be attempted in the direst circumstances.
If your player has been careful and sparing with his magic use then yeah, there's a decent chance that he'll have made it that far without triggering Tzeentch's Curse. If he's only thrown two dice, say, ten times, then his chance of not getting a curse is (9/10)^10=35%. That's not completely unreasonable. He's been a little lucky, but not so much as to be dumbfounded by it.
Your player's been smart about his use of magic. Good for him. That's one of the things that makes the WFRP universe tick.
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Piero S. P.
Italy
Turin
"If our gods and our hopes are nothing but scientific phenomena, then it must be said that our love is scientific as well." - L'Eve Future
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It is a nice system, still I believe, in some way - to a visceral level - it hasn't been properly modelled.
Would you have any suggestions, statistics-wise, to make a push-your-luck variant?
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"If our gods and our hopes are nothing but scientific phenomena, then it must be said that our love is scientific as well." - L'Eve Future
