d20 - Spell Prerequisites
So for those of you GMs who are tired of all those pesky game-breaking spells, you've probably resorted to one of two measures to counteract them for storytelling reasons:
1) You only play low-level games or E6 games where players can't get those high level spells.
OR
2) You ban those spells or homebrew stuff that specifically negates those effects.
The only other alternative is to let players break the game, and no good GM really wants that. (unless you're playing a comedy game, in which case who cares, right?)
I would like to propose an alternative to balancing high level magic:
SPELL PREREQUISITES
Just as warriors have to meet prerequisites for feats, now spellcasters must meet prerequisites for high level spells.
SPONTANEOUS CASTERS
In order to learn 2nd-level spells and higher, one must first know a spell of the same descriptors and school of 1 level lower. So the 6th level Sorcerer that wants to learn Fireball (a 3rd level Evocation [fire] spell) must first learn Scorching Ray (a 2nd level Evocation [fire] spell) and in order to learn Scorching Ray they must first learn Burning Hands (a 1st level Evocation [fire] spell). This continues all the way up and down the chain from 1st level spells to 9th level spells (although 1st level spells have no prerequisites).
If a player finds that there IS no spell with matching school and descriptors available, a GM may allow another spell of their choosing that suits the concept or homebrew a spell for them on a case-by-case basis.
PREPARED CASTERS
Prepared casters aren't limited to spells known like spontaneous casters but they are limited to what they can prepare in a day. In order to prepare a Fireball spell for the day, the wizard must first prepare a Scorching Ray and in order to prepare a Scorching Ray, they must first prepare a Burning Hands and so on and so forth. They may prepare any number of Fireballs per 1 scorching ray and 1 burning hands they have prepared, so long as they have at least 1 chain.
HOW IT WORKS
By restricting the conceptual types of magic spellcasters can create, we do 3 things:
1) Limit the power of a spellcaster: They still have powerful spells, but they don't have every spell in the book. They are more limited on what they can cast based on a single unifying concept (is he a fire-type mage, a necromancer or whatever). If they want powerful spells, they have to stick to a concept and this makes them slightly more predictable allowing the GM to create scenarios that offer them a challenge. If they choose to be versatile, then they will not learn as many high level spells and instead waste their high level spell slots on learning low level spells (which for those of you who didn't know, you CAN do that).
2) Solidify a concept: By locking in magic to grow in a chain (or tree in some cases) the spellcaster is forced to choose between being versatile with lots of lower level spells or having powerful spells that follow a single concept. This way they are not just Sorcerers and Wizards that can do whatever they want whenever they want, they are Necromancers, Pyromancers and Enchanters and so forth who have honed their skills through practice and specialization.
3) Level the playing field: One of the advantages spellcasters have over other character archetypes is magic, yes but also versatility. Spellcasters could pick spells at whim with no Intelligence or skill rank prerequisites like the feats and some class features that warrior and rogue types need. A spellcaster could select JUMP as one of their many spells while the rogue and warrior have to invest large chunks of their skill points to get half the effect. This way, spellcasters have to follow paths just like everyone else. They still get the advantage of magic, but now they have to plan ahead and "earn it" just like everyone else does.
Disclaimer: This does not PERFECTLY balance spellcasters with non-spellcasters, that's pretty much impossible and not the point. However, it helps GMs to balance the game-breaking spells by making the spellcasters more predictable or weaker. If they want to know every spell in the book, they'll be falling behind on power and if they want to be powerful, they'll be forced to keep a particular TYPE of casting.
