Decoding MP from Spell Descriptions
On the heels of the last post https://herdingdice.blogspot.com/2023/06/decoding-mana-point-and-target-number.html, I used the data and attempt some multiple linear regression. It was rough, but I found something to start from. I only used 44 of the easier spells to decipher, mostly damage spells. There are a lot of spell effects that I would have to put a lot of opinion into their numerical values so instead of opinion I just cut them from the analysis. I ended up with three basic parameters that one can use to ball park home brew your own spells decently close to rules as written.
The Simple MP Guide for Homebrew Spells
- Every d6 of damage or healing or direct value costs 1MP (1d6 = 1MP, 2d6 = 2MP, 3d6 = 3MP)
- if there is a +1 or +2 type of effect round up to 3.5 for 1MP cost
- Every 10 yards of range costs 1MP (round up to nearest multiple of 10)
- Every 10 yards of area of effect range costs 1 MP
- for spells defined with radius the range is the radius
- for spells defined with rectangle, the range is the length of the longest side
- Any test that gives a chance to lower the value can be ignored for simplicity. So instead of lowering the overall value we will simply charge for the best effect
- Penetrating damage increases spell cost by 3MP
Range and Radius
The idea that 10 yards is 1MP comes from the regression math. It was a significant parameter with a coefficient of about 0.1 which means each yard in the data contributes 0.1 MP or 10 yards is 1MP. This is a satisfying round number and plays well with the existing spells.
MP SP relationship
Using the spell stunts we can see that a 2SP to 1MP relationship exists by looking at "Skillful Casting" and "Mighty Spell". This would indicate that any additional effect that you find under stunts could be applied to spells for that. For example Knock Prone costs 2SP however you could add it to a spell for an additional 1MP.
Penetrating Condition
Many spells have penetrating damage which isn't clear what the cost should be. However since the maximum AR value is 10 from heavy plate and adversaries don't break 10 either (exception with or c warlord from FAGE companion who had magic plate armor of 13) we can then use 10 as the maximum potential value of penetrating damage. If we map 10 value with a 3d6 roll average of 10.5 we can safely price penetrating of 3MP. I think this would also be useful for stunts since pierce armor exists. A penetrate stunt could cost 3x2 = 6SP and the pierce stunt could cost have that for 3SP (current rules are 2SP)
Conflicts To Resolve
Powerful Casting implies 1 SP per spell power, but spell power is 3d6 + Willpower + Focus which implies that 1SP would equal 1 Willpower. And during leveling 1 Willpower adds 1MP to your pool. It would seem more equivalent if you also spent 2SP per spell power improvement
If 1MP = 1d6 then lethal spell (and lethal blow by proxy) should just be 4 SP instead of 5. I think this is fine and opens up a 6SP for 3d6 damage option for both spell and combat stunts.
Range of 10 yards to 1MP doesn't match well with Skirmish. If you use the 2SP to 1MP model a 2SP skirmish should have a range of 10 yards. Skirmish moves 5/10/15 yards for 1/2/3 SP
Examples
Flame Blast
- 2.3 MP - 2d6+1 = 8/3.5 MP = 2.3 MP
- 0MP - for the range but since it originates from the character the range is zero and MP is zero
- 1MP - for the area using rectangle rules, 8 yards is the longest dimension, round up to 10
Total = 3.3MP but round up to 4MP. This makes it the same as in the rule book. There is room to buff the spell to remove the round, ie 3d6 damage instead of 2d6+1.
Healing Touch
- 1MP per 1d6 healing, that's it since there is no range. Same as the rule book.
Healing Aura
- 1MP for each 1d6 of healing
- 1MP for area of effect using radius rules
Total then should be 2/3/4 MP for the three ranks but instead ranks 2 and 3 are 4 and 8MP. I wonder if "Lethal Spell" type of reasoing is instead being used for the additional power. It's 5/2 extra MP for another 1d6 of area value. So lets leave rank 1 alone. Then rank 2 assumes 2.5 extra MP for the 1d6 boost for a total of 4.5 MP. Then rank 3 is five extra MP for 2+5 = 7 MP. Rounding up ranks 1/2/3 of healing aura should be 2/5/7 MP
Whirlwind
- 3MP for 3d6 damage
- 1MP for 4 yard radius
- 5MP for the 50 yard range
- 1MP for the knock prone
Total is 10MP rounding everything immediately and gets you the same MP as original.
This is really cool. I'd love to see your excel file and the data more. Does it all seem to align well enough to possibly imply Green Ronin might have been using these numbers on their own? or do you think they did it in a more intuitive manner?
ReplyDeleteIt fits decently well with an r squared of around 0.6. While not complelely explanatory it is a strong indicator of positive correlation. In other words higher TN tends with higher MP. I don't think GR has it's own formula as the spell TN/MP would have a much higher correlation. I think they may have a few standard spells as a starting points and writers are encouraged to use them only as loose guidelines. Honestly it may be a valid business plan as you can only sell a rule set once, but you can sell many more books of content. Having a strong and obvious spell system would allow easier homebrewing and not need as much content books.
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