So after many years away from the d20 fold, I'm returning under the mantle of Pathfinder. I'm quite enjoying the system, but I wanted to seek the advice of these boards' more august and knowledgable members on a matter of converting a game world's idiosyncracies.
(Apologies if this sort of post is more appropriate to Advice than Conversions.)
I've been a fan of S. John Ross's Uresia: Grave of Heaven setting since its BESM days, and with the recent release of its second, systemless edition, I'm happily whipping up notes for running Pathfinder games in the world. There are lots of similiarities with bog-standard D&D, but lots of important differences, too. Most of these I'm so far finding easy to reskin or otherwise cludge together, but I wanted to see what y'all thought about a couple issues with the way magic works in the world.
First up, the setting is highly magical. There are repeated references to "hedge magic" being practiced by nearly every citizen in the world, from sailors knowing knot-tying spells to simple housekeeping charms. What's the best way to represent this mechanically?
Second, emeralds. Regular emeralds, especially once cut and polished, are batteries of magical power and are easily the greatest treasure in the world. The physically bigger the emerald, the more magic one can tap from it. The largest emeralds power great enchantments and magical devices. It is possible to overtap an emerald, however, and burn it out like a light bulb. No idea how to handle this one--are there any PF/d20 supplements/rules that deal with magical batteries that can be overused and burn out?
In my mind, "hedge magic" would be the equivalent of "cantrips/oracles", i.e. zero level spells.
Mage Hand could accomplish quite a bit, but if you wanted even more specific spells (like your 'Tie Knot' example) that could easily be thrown in. If you happen to have access to a copy of Rolemaster's 'Spell User's Companion' (orig. pub. date 1991), it has what they call 'Prosaic Lists', lists of those kinds of mundane everyday workman type spells. The system is significantly different from D20/PF, but spell concepts for this sort of thing should be simple enough to convert.
As for the emerald battery concept (cue Green Lantern), I'm not aware of an entire system devoted to that. The 'Pearl of Power' items in PF CRB allow the user to instantly recall one spell of appropriate level which the caster had prepared and cast, allowing them to cast it again (i.e. it is re-prepared). That fits the same logic, albeit for the caster, not for an item. You can read up on the Pearl of Power on the D20 SRD site, including costs for each level of pearl. You could also include higher cost emeralds to provide charges to items (similar to how casters may recharge charged items using spell slots on a daily basis) and perhaps even to the level of providing "permanance". Of course if the emeralds are as exorbitantly priced as you say, you could always add to the cost as needed to suit your desired economy.
It's been quite some time since I read Uresia. Can people use emeralds to power their own individual magical abilities? If not, the magic battery aspect could just be assumed to be part of the cost of making magic items, constructs, and so on.
If they can be used for personal abilities, you could compare what they should do with pearls of power, rings of wizardry, certain ioun stones, cognizance crystals (psionics), and other similar items.
In my mind, "hedge magic" would be the equivalent of "cantrips/oracles", i.e. zero level spells.
I'd had this thought, too. I was thinking of maybe making 0-level bonus spells available to any character with a high enough INT or WIS, with choices available from the wizard or cleric lists, respectively, and per-day casting limitations similar to a sorcerer.
Can people use emeralds to power their own individual magical abilities?
Here's what the book has to say about the matter:
Wizards wear ordinary emeralds as jewelry to supplement their reserves, while the rare giant stones can help level a village, raise an oasis in a desert, or fuel outsized enchantments like a suit of emerald armor.... Thrifty wizards disregard emeralds entirely, dismissing the baubles as more trouble than they're worth.... In terms of adventuring mojo, here's a benchmark for statting emeralds in game terms: giving an adventuring wizard a single caster's stone (one suited to them) should be roughly equivalent to giving a mercenary warrior a full rig of top-notch warrior's gear: heavy armor, a good sword, a stout shield, a sturdy horse.... That is to say, a single emerald has a genuine impact in terms of maximizing the wizard's potency, while multiple emeralds prepare him for extended challenges.
Pearls of power seem like a good model to start with. Maybe emeralds increase effective caster level? Or grant bonus spell slots? Or grant meta-magic feats? Burnout could be modeled with charges, I suppose--each time you tap an emerald for its bonus power, you use up one or more charges.