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Thread: A Design Guide for Homebrew Spells and Weapons

  1. #1
    Keeper of Secrets mdlthree's Avatar
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    A Design Guide for Homebrew Spells and Weapons

    This post is based on the analysis of the existing AGE spell and weapon mechanics (FAGE and DAGE). There are six elements of choice when creating a spell:
    • Direct Effect
    • Resist Chance
    • Effect over Time
    • Effect over Area
    • Range
    • TN or Target Number

    The direct effect, resist chance and effect over time have a multiplicative relationship. The range and effect over area components are added on top. The total of these components create the raw MP value of the spell. The raw MP is then multiplied by the appropriate TN probability and an additional value of 4 is subtracted as action credit. The resulting value is rounded to create the final spell MP.

    Direct Effect
    • Take the average of any dice roll as the value
    • Any buff or debuff value is 1 to 1 with spell value
    • Stunt point bonus are valued at 1 per SP
    • Damage bonus, MP, HP, AR, focuses, ability scores also are valued at a 1 to 1 scale
    • Penetrating damage is an extra 4 value

    Resist Chance
    • Any resist chance can be applied as a 50% reduction of direct effect cost.
    • If the effect is more complex with some remaining effect if the resist is successful, then you add together the direct value of both the success and fail cases and then apply the 50% reduction (like Flame Blast).

    Effect Over Time
    • The most effective rule I found for effects over time is to double the direct effect regardless of the length of time for the effect. When trying this rule on all the different duration conditions like rounds or minutes or hours, twice the single round cost is enough to capture an accurate valuation of the effect.

    Effect Over Area
    • I found a simple valuation for AOE component. The value of AOE is the number of affected squares minus 1 then divided by three.
    • For a spell with a radius AOE description I found a formula that counts squares that works for any movement rules. The number of squares for a radius spell is 3*R2 + 3*R + 1. When using this with previous value formula it reduces to R2+R

    Range
    • The value of range is 1 for every square (2 yards) in distance minus 1 (for the adjacent square)

    TN Target Number
    This one represent how easy it is to cast the spell. For zero ability character, a TN 11 spell has a 50% cast success chance, a TN 13 has a 25% cast success chance, etc. It is up to the designer to decide how hard to make this number. TN affects how much the spell will ultimately cost as well.

    Putting It All Together - Lets pretend to invent the Firestorm spell using these simple formulas:
    • Direct Effect - 3d6 damage + 2 for a failed dex test, total of 10.5+2, or 12.5
    • Direct Effect - 3d6 damage + 0 for a successful dex test, total of 10.5
    • Resist Chance - The two cases times 50% is (12.5+10.5)*0.5 is 11.5
    • Effect Over Time - None
    • Effect Over Area - 4 yard radius using the formula for counting squares is 22 + 2 is 6
    • Range - spell has a 50 yard range or 25 squares. 25 - 1 is 24 value for range
    • TN - firestorm should be a tricky spell so lets set it at a TN of 15.
      Raw MP : 11.5 + 6+ 24 is 41.5

    TN 15 chance is 9.26%. Times that by 41.5 gives you 3.84. Minus the 4 action credit puts the final spell cost at -0.16 MP. Now this is something you can measure the appropriateness of the TN value. We really don't want a free spell. Let's punch in different TN until we get something close to 11MP like in the book. TN 13 is the closest with 41.5*37.5% - 4 is 11.56 or 12 MP with rounding.

    Weapon Damage
    • Weapons are just simple spells with 1 range.
    • Longsword - 2d6 or 7 Direct Effect. TN is 10. Final MP is 7*62.5%-4 is 0.375 or 0MP. The 0MP for weapons is really the minimum strength.
    • 2H Axe - 3d6 or 10.5, TN10. 10.5*62.5%-4 is 2.56 or 3MP rounded (3 Min Str)


    So that's how the system works so far. I have some ideas on how technology (like bows) would contribute to value through their cost in gold pieces.

    PS - to look up what is the % for a TN, go to anydice.com punch in 3d6 to the calculator and look at the "At Least" table.
    Herding Dice - A tumblr where I put things about Adventure Game Engine design.
    Adventure Mechanics - A set of house rules for the Adventure Game Engine that focus on mathematically informed opinions for balance and extension.

  2. #2
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    Re: A Design Guide for Homebrew Spells and Weapons

    Don't forget reload times for ranged weapons.

  3. #3
    Keeper of Secrets mdlthree's Avatar
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    Re: A Design Guide for Homebrew Spells and Weapons

    Quote Originally Posted by shonuff View Post
    Don't forget reload times for ranged weapons.
    I was reminded about a fairly spirited thread about an earlier attempt at ranged weapons that wasn't so successful - Alternate-Model-for-Movement-and-Ranged-Attacks-Balance. It was a useful discussion that did help inform how I treat the range of spells. Turning these ideas back toward range weapons I have thought of how to characterize them with these formulas.

    It starts with what I found useful to value actions. The minus 4 from the spell formula represents the value I place on a minor action. A major action I define with a value of 6, 4 from the base minor and 2 from the chance to generate stunt points. As a reload is a minor action we need to allocate those 4 reserved value points into the cost of the attack. This would change the action offset value from minus 4 to minus 8. That leaves a lot more room for the ranged attack to spend on the range portion of the "spell".

    To re-create the short bow (1d6+1) we first use the spell formula like a melee weapon (action budget of 4, TN of 10) to find out what its minimum strength would be. This happens to be the same value as reported in the rule book as -1. Next we use the formula again except with an action budget of 8 and crank up the range on the spell to just before the new minimum strength hits -1 again. The formula allows a total range of 8 which we will use as the short range for the short bow at 16 (8*2) yards. This also happens to be the same short range as the rule book, so far so good.

    To find what the long range of the bow we can start using the rule book penalty of -2 to hit at long range. This will bump up the weapon TN from 10 to 12. Increasing the TN decreases raw cost and allows the range to be cranked up further. This pushes the long range shot of the short bow to 16 squares or 32 yards. This is also the reported value in the book, so score another bull's eye for this formula.

    One thing that is under powered is the "Aim" minor action when using the assumption that a minor action is worth 4 value points. Aim could be change in one of two ways. It could be halved in cost (half your movement) to perform the aim, or it could be double in value (+4 to hit) to make up the extra cost. With a full +4 to hit we could change the long range penalty to -4 so that aim and long range have a nice canceling effect. This would push the long range TN to 14 and increase the max range on the short bow to 42 squares or 84 yards. This extra long distance may please some of the people in that unsuccessful thread with some reasonable long range values.

    Here is an experiment with the long bow. Our expectations for it are at least more range but if we also give it more damage the spell formula cannot increase it's range as much. In fact the short range result is only at 9 squares (1 more than the short bow). If instead we keep it at the same weapon damage as the short bow (1d6+1) we increase the range until we hit the minimum strength of 1. This results in a short range of 11, 3 more than short bow. If we add increase the min strength to 2 we get a short range of 13 squares (26 yards) which is the range value of the rule book. At long range this +2 strength long bow (with the -4/+4 aim/penalty) is 61 squares or 122 yards which is much closer to historical long bow range. Just for fun, let's create a long bow that does 1d6+1 damage but has a minimum strength of +5. Short range is 17 squares (34 yards) and the -4 long range is 79 squares (almost 160 yards).

    One more quick run with a cross bow as an example of the major action reload benefit. At +1 min strength, 2d6+1 damage, the short range on the crossbow should be 11 squares (22 yards) and the -4 long range is 63 squares (126 yards).

    With this spell formula and adding the minor action as pure range credit we can create range weapons that are balanced against melee weapons and spells since they all use the same formula.
    Herding Dice - A tumblr where I put things about Adventure Game Engine design.
    Adventure Mechanics - A set of house rules for the Adventure Game Engine that focus on mathematically informed opinions for balance and extension.

  4. #4
    Keeper of Secrets mdlthree's Avatar
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    Re: A Design Guide for Homebrew Spells and Weapons

    10 months later I have made some improvements on this topic. The general categories remain similar.

    Primary Spell Value - includes damage or healing effect (like single target), resist effects (an simple 50% value reduction), and duration effects (a multiplicative factor of 3.5)
    Secondary Spell Value - includes range (yards / 2), AOE cost (8 if an AOE spell), AOE radius cost (yards / 2).

    The TN of a spell can be calculated in two ways. First is that the designer just sets it to whatever. Second is to use the table from this post to determine the optimal value. What is different from the previous method is that now I only determine optimal TN using the "Primary Spell Value". I found that including those elements in the secondary spell value category could quickly skyrocket the value of a spell and force the optimal TN to be quite high. So I split the values in two parts and I also simplified the AOE formula. Instead of a quadratic component I changed it to a flat value of 8 plus the radius intended for the spell. If the spell is a funny shape like a rectangle you can just back calculate the radius of a circle with equal area. Like Shock Blast with a 6 by 6 area, find its equivalent radius with SQRT((6*6)/PI) ~ 3.38.

    The duration factor comes from the analysis of combat pace which determines that 1 damage buff is equivalent to 3.5 HP. The 1 damage (or value) is constant per round while the 3.5HP represents a total for the encounter. For any type of duration effect I use this 3.5 factor on the spell value. There is one exception and that is for spells that have a passive effect but the target gets a chance to resist it every round. This is the situation of Zeno's dichotomy paradox where you move half the remaining distance each turn. The perpetual resist effect is similar where the compounded 50% chance to resist add up to one (eventually at infinity). So that case I do not multiply by 3.5 nor do I discount the spell value by 50% for the resist chance. Not a lot of spells have that feature but enough to treat it properly.

    So after finding the optimal TN (or just picking one) you multiply that chance of success by the total of the primary and secondary values. Then you subtract 4 value for every action that spell required to cast. 1 action for most things, 4 actions or 1 minute casts, etc. Any remaining value after this equation becomes your minimum STR or MP cost.

    The value of an action is 4 (minor or major, this is my simplification to the action economy). That means the value of a turn is 8. If a spell was to render a target with no actions for a turn that would cost 8 value. If the intent was to coerce the target to take a turn against their will that would be 8 to cancel their action and 8 more to empower them to act for you for a total of 16. A spell like that would likely also have a resist feature reducing the total value by half back to 8 for TN12 0 MP, but if you didn't, a no resist full turn mind control spell would be a baseline of TN 15 with 0 MP cost (because that's how optimal TN works). Mind control no resist for the full encounter would be 16*3.5 for 56, which puts it at TN16 0 MP. Any range on that spell then would increase the secondary cost but not increase the TN because I have separated them.

    I have gone through the exercise of recalculating all FAGE and DAGE spells with this system using the optimal TN strategy. Some results are:
    • Reduced average MP cost for FAGE by 3, and DAGE by 7
    • Reduced average TN cost in FAGE by 1, and in DAGE by 3
    • Out of 176 spells, 69 spells across DAGE and FAGE could have their MP costs reduced to 0 with optimal TN choice.
    • The guidelines were simple to follow and I could re-balance all 176 spells in a few hours and only a few of them needed some sort of rework (some DAGE spells are far too complicated for their own good)


    If anyone is interested in seeing the spell list please PM me on the forums. Or maybe a forum moderator can let me know if the spell list can be shared on the forum in full.
    Questions, comments, I would love to hear them.

    PS - reloading a ranged weapon would count 2 actions towards the whole spell. Also all physical attacks are calculated against a spell TN of 10, not optimal TN, because of the way the defense works.
    Last edited by mdlthree; 10-15-2017 at 09:59 AM.
    Herding Dice - A tumblr where I put things about Adventure Game Engine design.
    Adventure Mechanics - A set of house rules for the Adventure Game Engine that focus on mathematically informed opinions for balance and extension.

  5. #5
    Keeper of Secrets mdlthree's Avatar
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    Re: A Design Guide for Homebrew Spells and Weapons

    Based on new research contained in this post - https://roninarmy.com/.../7185-Action-Value-Based-on-Passive-TN-and-Weapon-Design-Consequences - I have reduced my recommended action value from 4 to 3.
    Herding Dice - A tumblr where I put things about Adventure Game Engine design.
    Adventure Mechanics - A set of house rules for the Adventure Game Engine that focus on mathematically informed opinions for balance and extension.

  6. #6
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    Re: A Design Guide for Homebrew Spells and Weapons

    Rather than a spell creation system, I think you may have the starting point for a free form magic system, which I prefer over set spell lists any day. Mmm.....

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