Notes toward Spellcasters native to the world of Thaum.

This world doesn't observe the traditional D&D distinction between between arcane and divine casters. There are what we can call generalist spellcasters and there are specialist spellcasters, either focusing on a school or subschool of magic, or an element, or an animal spirit. And there are book-wizards and hedge-wizards. Book wizards can, in principle, cast any spell in the game, but at a cost. Hedge wizards are limited in the spells they can know, either to a thematic list or to a small group of the most common spells. (So there are hedge generalists, called warcasters, usually with savage tribes of one sort or another who aren't especially thematic, so they don't have a Fire Witch or a Thunderlord or a Grand Transmuter or a Bear Shaman.)

Spellcasters have spell slots (or maybe, maybe spell points) and Spells Known according to their level. Specialist casters can never learn spells outside their specialty. (This may be amended with a list of "universal" spells--especially Dispel MAgic or a substitute). If a spell is not on your Spells Known list, you can still attempt to cast it from a spellbook (book-wizards) or free form (hedge-wizards)

Spellbooks aren't something you can just port around--they're massive tomes, each containing 12-15-20 spells united by a school or theme. They count as magic items (cost as a scroll of all those spells), and are often "masterwork items" on top of that (+2 to Spellcraft checks for each doubling of the cost. Money is magic too).

Off list casting. When casting a spell from a spellbook, make the Spellcraft (DC 15 + SL) check once for each spell level. Take d6 backlash damage for each spell level when the process is complete and the spell is either cast or fails.

So a generic 1st level Apprentice (+1 rank, +3 class, +1 INT = +5) casting a 1st level spell (DC 16) has a 50% chance of success unaided (and a 100% chance of 1d6 damage). A 2nd level Journeyman (+2 ranks, +3 class, +1 INT, +2 synergy = +8 ) has a 65% chance, a 3rd level Master has a 70% chance.

The 3rd level Master has a .60*.60 = 36% chance of successfully casting a 2nd level spell from a spellbook.

A 5th level caster (+5 ranks +3 class +2 Int +2 synergy +2 materials = +14) attempting a 3rd level spell (DC 18) has a (.85^3 = 60% chance)

Specialists get a +2, which comes in really handy. Warcasters just get the shaft.