Rules light/Rules tight magic

[Prak]

How would one go about making a light rules system of magic for a game, without creating a system of magic so broad that starting characters can encase people in lead with only a modest investment?

[angelfromanotherpin]

That's going to depend on the underlying general system. For instance, one version of Fat3's magic system included 'spend a fate point to use your magic skill as any other skill for one roll,' so Guns for a firebolt, or Stealth for a cloaking spell. But that relies on the fixed skill list and the fate point mechanic that the rest of the game is based on.

[Lokathor]

In general, I'm not sure that you can have improv magic do arbitrary effects without having a part of it be "and then the MC decides if it's all reasonable or not".

While I'm not personally put off by this idea, lots of TGD gets really upset by needing to make your rules do a function call out to MTP-land.

[crasskris]

Have a decent write-up of each power.

Since most forms of magic offer simply new, fictional tools to manipulate existing laws of nature, you'd need to describe these tools properly.

If molding lead without heating it is part of the tool, you'll need to define how much one can mold and/or move in what time, and how additional skill affects the volume of the effect and/or the time needed.

If done carefully, the restrictions should enhance creativity instead of blocking them, and, more importantly, free a lot of headspace for the MC during the game.

You'd basically need to do the same work for every other skill in the game, but skills like running or climbing exist in our world and are thus well known and should be easy to interpret. But in a world without running you'd have to write up a descriptions of it's options and limitations, too, if you'd want to use it. Just writing "You walk faster" probably won't do.

You'll probably end up with a full page or more per power, not game rules, but in-game rules that serve as a basis for judging the use of the power by player and MC.
For your example, the base effect of the lead molding power could allow to mold a few pounds with the same speed and in the same form a smith could work an already heated version of the material. It would take an expert in lead molding to form a person-sized mold at once or use it quick enough to have battlefield use, and a master to do both at the same time.

[Grek]

I talked about this a bit in the Notnia thread. You need an effects based system in order to get something reasonably rules light. You pick out the game mechanical effects of your spell and declare this to be the spell's "Intentional Component" - what the caster intends for the spell to accomplish once cast. You then talk about how that particular magic user would use their particular brand of magic to go about accomplishing that intent. This is the "Accidental Component" of the spell - the parts that are based on the caster more than on the spell. Counterspells and magical defenses are based off the Accidental Component, so Fire Mages and Ice Mages are excellent at countering each other, and your group needs to have a discussion about how well two Necromancers are at undoing the others work.

I didn't know it at the time, but what you basically want is the Mutants and Masterminds power stunting system. The Intentional Component is your Effects and the Accidental Component is your Descriptors. Your modifiers are based more on the source of the spell, with Wand Magic having Removable while Ritual Magic has Distracting and Concentration.

[OgreBattle]

Don't think in terms of magic vs mundane, instead think of it as characters using different resource systems to accomplish similar goals be it social, combat, or exploration.

[Dogbert]

If you don't want players to "encase people in lead with only a modest investment" then state a generic list of effects by hierarchy then assign costs accordingly, something like:

(in no specific order)
-Trivializing a task that would take hours using mundane skills (divinations, flight/teleport, polymorph, etc).
-Trivializing a task that would take days using mundane skills.
-Trivializing a task that would take months using mundane skills.
-Trivializing a task that would take years using mundane skills.
-Damage effect (per die/+1/etc).
-Buff/Debuff (Duration: Scene(s)): per die/+1/etc. (competence enchantments/polymorph/etc).
-Buff/Debuff (Duration: Day(s)): per die/+1/etc.
-Buff/Debuff (Duration: Permanent): per die/+1/etc.
-Healing: per die/+1/etc.
-Resurrection.

Mind you... I might end up using this myself (provided I take the time to debug and polish it).

[Krusk]

Couldnt you also decide its ok that your magic system isnt complete. Just say there are x spells. And a pc can learn y (y<x). Your spells do specific things that youve deemed balanced and ok. They do not do things that you do not want them to do.

Then when a player says "i want a spell that teleports me" you can say "well youve got 3 options, 1 requires line of sight, 1 lets you run through the astral plane so you go at x 1000 speed but still have to actually walk there. No flight and only seems like teleportation to those observing, and the last requires you to swap places with a willing party." Then if they want something else, its too bad. No one wrote that spell and for whatever reason its impossible.

So basically the 3e way, but without writing bad spells.

I just cant see a build your own spell system working in any form of rules light game, if you want anything cooler than x damage of y type. Pick x and y from lists. Especially if you want to keep it from overshadowing every other option.

[hyzmarca]

There are three classes of Magic, Hocus-Pocus, Abrakadabra, and Shazam.

Each class has some flavorful differences that don't matter for their end effects. Everyone has six stats related to them, their offense and defense stats.

All magic use is an opposed roll, your offense in the appropriate magic stat vs their defense. Every success you get is worth one point of their damage track. You get to make up whatever flavorful explanation you want for their current status. You can also, if you wise, cause less damage than you rolled. So encasing someone in lead requires pushing their damage track to incapacitated, and the lead is why they're incapacitated.

Interactions with mundane stats and actions don't happen because everything is considered magic and you have no mundane stats and take no mundane actions.

That's, um, incredibly rules lite, I think. It also means that you can litterally do anything unless opposed by another player.

If this is an issue you can have the DM roll an arbitrary difficulty score in opposition, when there is no opposing player or set an arbitrary difficulty threshold, but that's arbitrary.

[JonSetanta]

Use Final Fantasy as a basis.
Make sure you include mana-based and free casting.

[Blade]

You can have a system where the "mana cost" is based on the impact of the spell in game. Lightning your cigarette with a fire effect is free if it's just for the fluff, it has some cost if it's to get a positive modifier for a social check and it has a higher cost if it's to get the bandits to let you pass.

The drawback with that kind of system is that it doesn't reward creativity (unless you reduce the cost for a clever idea) and that it just means you have to max out your mana to "win the game". Adding some constraints like a cost to get mana and/or constraints for the spells (such as "needs to be fire-related", "must respect mass conservation laws", etc.) can make things more interesting.

[RadiantPhoenix]

Every rule you don't write in the books is a rule the players have to make up as they go along.

Generally, this power and responsibility will fall to the Dungeon Master, because she is the one who's already handling a plurality or majority of the rules you did write.