Re: Converting Shadowrun Magic to GURPS
 

In most versions of Shadowrun, you had access to a lot of spells you could cast at zero drain, but the difference between average and exceptional wasn't really that high, Will 3 vs Will 6 is only about 1 success. I would probably go with Will rolls at fairly high penalties to resist drain, and then lose fatigue based on some divisor of margin of failure

Re: Converting Shadowrun Magic to GURPS
 

Crap rolls could still make even the simplest spell cost drain. And of course, no need to mention the bad mechanics where greater ability means greater chance of botches.

Re: Converting Shadowrun Magic to GURPS
 

I still feel like importing an extra drain roll per casting is importing mechanics rather than flavor. What's needed is that Will have some (prefferably variable) effect on final FP cost. Doing a whole nother roll to achieve that seems to me to be the clumsiest possible implementation.

Though to be fair my interpretation of "flavor" is "what appears in fluff text or novels," generally.

Re: Converting Shadowrun Magic to GURPS
 

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.

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?

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.

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?

Re: Converting Shadowrun Magic to GURPS
 

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.

Re: Converting Shadowrun Magic to GURPS
 

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.

Re: Converting Shadowrun Magic to GURPS
 

Traditions should be fairly straightforward as a Higher Purpose, with disadvantages to balance it out.

That wouldn't be far off - at least in 4E, shadowrunners start off with the points to be viciously competent world-class examples of their profession.

And if cybernetics need to be paid with points, then 350-400 sounds about right for the Street Samurai to have some decent augmentations.