Converting Shadowrun Magic to GURPS

[Jürgen Hubert]

Another idea: The Force of a spell represents the maximum Margin of Success you can have on your relevant skill roll. This Margin of Success is relevant for the overall damage of combat spells, resisted rolls for illusion/mind control spells, and so forth.

If your actual Margin of Success is higher than the Force of your spell, then any additional points of Margin of Success reduce the fatigue cost/drain of the spell.

So if you want to "play it safe", cast the spell at a low Force rating and you will have very good chances of reducing the fatigue cost of the spell. But if you want to go all out, cast it at a high Force - but then some fatigue is almost guaranteed.

This also simplifies the success roll and the drain resistance roll into a single roll.

[Crakkerjakk]

Originally Posted by Jürgen Hubert

I'm still divided over that. Some people should have an easier time resisting drain than others, but basing everything on Will would probably be too unbalancing, unless you are okay with all PC mages running around with Will 20.


Some further thoughts on how to do the conversion:

I will largely go with the Shadowrun 5E rules, since they are the most recent and more flexible damage levels are easier to port than the four damage levels of Shadowrun 3E and earlier.

In Shadowrun 5E, an "average human" has 10 physical damage boxes. After that, he becomes "dying".

In GURPS, I will thus treat those 10 physical damage boxes as 20 hit points, with each box representing roughly 2 hit points.

For statistical analysis purposes, I will assume that each Shadowrun die equals 1/3 of a "hit", or success. Thus, an average human - with a value of "3" in all attributes - will have one hit on most resistance tests.

I don't think it should be a design goal to match specific outcomes from one set of mechanics to the other. I mean, trolls should be able to shrug off quite a few light pistol hits, but the exact same amount as SR is unnecessary, IMO. I'd feel the same about spell damage levels.

I like the idea of Force capping MoS.

[Jürgen Hubert]

Basically, 20 points of damage would be my base value for "how powerful has this spell to be to take out an average guy with one hit". Let's examine some Shadowrun spells and translate them into GURPS states (complete with character point totals) and see if we can figure something out - since the damage types for GURPS are far more flexible than those for Shadowrun, it is my hope that we can come up with a system for far more flexible spell attacks based on Innate Attack than what is possible with the Shadowrun rules.

Let's start with a "Mana Bolt". It only damages physical objects, which makes it Toxic damage [4/level] - but we need to do 6d-1 toxic damage to get an average of 20 damage, which makes the base cost 4 x 5.7 = 22.8 CP.

It ignores all armor, which makes it a Malediction - and since it is Line of Sight, we give it the long-range modifier (+200%). Mana spells also Affect Insubstantial targets (+20%), which brings the total to 73 CP.

This is the equivalent of a Force 10 manabolt which has attained 10 net successes (a tall order for a spellcaster, but let's leave that aside). This would have a drain value of (Force -3) = 7.

A "Power Bolt" would look fairly similar, but start out with either "crushing" or "piercing" damage for 5 CP/level. For 20 damage this would increase to 5 x 5.7 = 28.5 CP, which (with the Malediction, but without Affects Insubstantial) brings us to a total of 86 CP.


Now let's get to "indirect" spells that create a physical force instead of working like a malediction - picking the "Flamethrower" spell. This is burning damage, for 5 CP/level which again brings us to 28.5 CP for the base damage. Furthermore, it counts as "Guided" (+50%) since there are no range penalties. While it is hard to model attacks with infinite range in GURPS, let's say that this spell has a range of 200 yards, which is sufficient for most purposes. Starting out with the 10 yards for 1/2 D and the 100 yards for Max, we need to bring both of these values to 200 so that the spell reaches that far (+5%) and can hit the target within one round (+20%). Furthermore, indirect combat spells in Shadowrun are armor-piercing by default - so let's give it an Armor Divisor of (2), for +50%. This adds up to a total of 65 CP.

As an indirect spell, a Shadowrun mage casting "Flamethrower" needs to end up with a Damage Value of 11 (since the average human with Body 3 will roll one success in resisting the damage). This is doable with Force 6, resulting in a drain value of (Force - 3) = 3.

[Jürgen Hubert]

So what's my take from all this math? Well, I think my suggestion for linking force and drain reduction on the success test is a good one. However, this will also make it somewhat harder to reduce Drain in GURPS than it is in Shadowrun - since if you don't manage to reach a Margin of Success higher than your Force, your Drain won't be reduced at all.

So, assuming that we treat Shadowrun Stun damage and GURPS Fatigue as identical (which should work reasonably well - an "average human" has 10 of either), then the Fatigue values should be slightly lower in the GURPS rules than their equivalent drain rules.

Right now, I am considering 15 CP in an Innate Attack = 1 point of base Fatigue. Furthermore, you need 1 level of spell Force for each 15 CP in Innate Attack you want to deploy - and if you fail to reach a Margin of Success equal to your Force, the Innate Attack acts as if it was worth less CP.

This of course would mean that we would have to create tables for spell effects - listing the damage / other effect for each point of MoS reached.

This rule might also be extend-able to other spell effects - figure out what the CP value should be, and derive the fatigue cost based on that (as well as what the required Force levels would be).

Finally, I think 5 CP per spell learned would be a good costs for spells.


What do you think so far?

[Fred Brackin]

Originally Posted by Jürgen Hubert

Let's start with a "Mana Bolt". It only damages physical objects, which makes it Toxic damage [4/level] -

No, Characters p.62 specifies that Toxic damage never affects Machines. Machines are "physical objects" so Mana Bolt can not be Toxic.

For "generic" damage I think you might be looking for Crushing with No Knockback

[Darekun]

Wow, what timing! I've recently been starting up a GURPS: Shadowrun side game, chargen is almost done. (I'm the GM.) However, I took a rather-different tack with magic, calling for spells to be built and largely leaving it at that. A "proper" conversion would prebuild the Berkeley Grimoire spells, and probably standardize some modifiers in the process. I also used some different assumptions, so let's see…

First, let's get this out of the way:

• Pretty much every time I've seen an SR -> GURPS conversion, I've seen GURPS players discounting what I consider important parts of SR's magic as "just mechanics". This is an assumption clash, akin to Dragonlance/Eberron vs other in D&D settings; SR is like Dragonlance and Eberron in that oddities of the mechanics are construed as oddities of the setting that are represented in mechanics(aside from quantization and straight-out bugs). GURPS tends to be more like the other D&D settings, in that mechanics and fluff are developed separately and then bonded. I am going to generally ignore "just mechanics" comments for this reason.
• One of the odd things about how it seems most people use Powers magic is they don't attempt to combine spells into a single magical ability; as a result, facing dispels comes out bizarre, and yet you're paying full price for that bizarreness. I generally assume that spells should be Alternates of each other, or some equivalent(my conversion uses a custom rule to avoid the oddities of "Did you last use an Alternate Ability or an Alternate Attack?"). The weakness this conveys is that anything that shuts down their ability to cast a spell shuts down their ability to cast spells, which I think is reasonable.

Originally Posted by Jürgen Hubert

- Each spell costs the same effort to learn, and there are no prerequisites.

- Spells are primarily balanced by how fatiguing they are.

These two suggest a "tack family" to me: Using Abilities At Default(p173, G:Powers) or Modular Abilities. The first is likely the simpler approach, so I'll use that.

Using Abilities At Default calls for a base ability to vary, and has a number of consequences we don't want as a result. In this case, it may be best to assume an implicit base ability, perhaps declared on the basis of -2 to the Will roll per 15pt(assuming 1 Force per 15pt of ability). Knowledge of the spell(a separate advantage, 5pt each seems reasonable offhand) determines whether the default is possible, and takes care of familiarity, so we can ignore those parts. From there it gets more interesting.

The Will roll to default is separate from the roll for Malediction or the like; for spells that don't already have such a roll, you can apply a Requires Roll lim. You can leave this optional, which basically means spells with no roll of their own will need higher Force and Drain for the same effect, which is reasonable.

The FP costing is worse of a fit. Using Abilities At Default has a base FP cost, and any further FP cost is chosen to improve the roll. You could simply let MOS reduce the base FP cost, which would work, but may change the feel in ways I can't predict. Alternately, you can treat the base FP cost as a penalty to the roll, and say FP cost is equal to MOF; this is closer in feel, but may be too swingy.

Using Abilities At Default caps the ability that can be produced. A different cap should be used; this also ties into overcasting. You may wish to define max "safe" Force as 1+Magery, with the spell switching over to HP Drain up to twice that. Personally, I like the switchover — it means magicians are likely to ignore overcasting except when they need it.

Anything I missed?

Originally Posted by Jürgen Hubert

- Low-Force spells are hard to detect, while high-Force spells are easy to detect.

It may be useful to define "Low Signature" to require a [Per + Force - range] roll to notice. Spells based on non-attack abilities may be able to take a -10% lim to get to this level.

Originally Posted by Jürgen Hubert

- For permanent physical alterations which are not directly damaging, artificial objects are harder to change than simple, "natural" objects. Cybernetic and other implants count as "artificial" and make it more difficult to cast such spells (such as healing spells) on their owners.

You may note that for my conversion, I created an Essence system in GURPS scale; this means spells can call for a roll of the subject's Essence. For an ORT equivalent, perhaps build in "Only On Natural" to some levels of the spell, so it must be cast at a higher Force to get the same effect on a cybered target?

[GodBeastX]

Having gone through the shadowrun book of magic with a fine tooth comb, I personally felt translating it over isn't viable. Much of Shadowrun magic is very much balancing mechanics, and others are lore mechanics.

For example, traditions play an important role in SR magic, and there's a great deal of difficulty representing that in a balanced way for GURPS.

The Thaumaturgy book gave me a few ideas for working SR magic into GURPS better. I thought about discarding the base statistic all together and making magery the defining stat for magic "Skills". 10 + Magery as outlined in Thaumaturgy.

Ideas I had for "Drain" were sorta like Threshold magic. But instead of a draining pool, that is basically your limit for magic before you're "Overcasting" and affecting HP. And something like every 5 energy you have to roll -1 against something or you lose a fatigue/HP.

One thing I've felt is, you probably don't want to use basic Magic as is. It is OP in some ways, and UP in other ways. Mages in shadowrun are devestating with AOE and damage effects, that is not really the case in GURPS basic magic. Especially considering the tech level of equipment.

[Jürgen Hubert]

Further thoughts:

- I'd say maintaining a spell is probably good for a flat -2 on all skill rolls.

- For casting spells, I'd split the relevant skills into these:

(a) Spellcasting, Counterspelling, Ritual Magic - these serve as caps for the other skills when engaging in a particular magical activity.

(b) Combat Spells, Detection Spells, Illusion Spells, Health Spells, Manipulation Spells - roll against the relevant skill when casting (or counterspelling) a spell of the appropriate type.

- Counterspelling: You can protect a number of people within your line of sight equal to your Magical Aptitude. Roll versus the higher of your Counterspelling or Spell Type skill. For each point of Margin of Success, you reduce one point of Margin of Success from the enemy caster. This is done after calculating drain for the other caster! However, each subsequent time you do this before it is your turn again you suffer a cumulative -3 penalty to your Counterspelling rolls.