To understand magic, understand that this setting is animistic. Every object has a life to it, a soul, if not necessarily bearing the same sort of mind or consciousness as a human-or, according to some heretical witches and shamans, this is the reverse, that all material things are the possession of souls, not vice-versa. In any case, this is not how most of human society views magic; indeed, this view is heretical among both most organized religions and sorcery communities.
All magic is derived from the same source, ultimately; soul energy. What makes one form of magic distinct from another is usually how this energy is acquired and channeled. Divine magic draws upon energy granted from outside sources, such powerful entities or environments. Sorcery is performed by altering an object’s own anima, thus causing a physical change as a reaction. Finally, Witchcraft is is channeling energy from inside oneself, though this inner magic is often attained by means that qualify as divine.
Even between these distinctions, there are two more major groups; the origin of the energy used to produce the change or effect. Ritual magic draws on the magic inherent in objects, taking advantage of environmental conditions and material components and is the most common type. Self magic, the rarest type, is magic that draws from one’s own soul. Then, there is magic powered by soul energy taken from other beings forcefully, either siphoned off or using an entire captured soul, and is the second most common.
Mechanically, we’ll be using the Spell Points and Vitalizing variants from Unearthed Arcana.
Wilders gain spell points as a Sorcerer does on table 5-3 in Unearthed Arcana (page 153), Clerics, Druids, Dread Necromancers, Erutides and Psions gain spell points as Clerics, Druids and Wizards do in table 5-3, Artificers, Bards and Duskblades gain spel points as a Bard does in table 5-3 and Paladins, Rangers and Spellthieves gain spell points as Paladins and Rangers do in table 5-3.
We are also using the Vitalizing variant as described on page 156.
The rules outlined about multiclassing under this variant, as outlined on page 156 are in effect.
Spell Points are restored as outlined on page 157.
Incantations are in use, as described on page 174 of the Unearthed Arcana.
Also to note, magic does not inherently need the standard components, such as verbal, somatic, material or focuses. These elements act as catalysts, reducing the amount of skill and energy to cast magic. The Still Spell and Silent spell feats do no exist.
A caster can only use one of any catalyst type for a given cast, though they may combine catalysts of different types in the same cast. The types are verbal, somatic, material, focus and environmental. Casting a spell without a verbal or somatic component increases the spell’s Spell Points cost by 2 (4 for without either) and increases the DC for Concentration checks to continue casting by +2. Casting without a called-for material component or focus doubles the base cost (not factoring in other increases such as casting without a verbal component) and increase the DC for Concentration checks to continue casting by +4. Adding a spell component or focus (as approved by the DM) when none is called for decreases the cost by -2 Spell Points (-4 for both, to a minimum of 0).
There will also be Taint and Sanity scores in this (pages 189 and 194 of Unearthed Arcana, respectively). The taint-based classes will get a bit of a buff and leniency on alignment (for example, Ashitaka from Princess Mononoke would have been a Tainted Warrior if he had used the strength from the blood-worm curse more than once), though it will pressure you about it.