Here is some open content from the RCFG Player's Guide:
Magic is a supernatural force that can change or defy the normal laws of physics within the campaign world.
Historically, magic was thought to follow “laws” of its own. The difference between the laws of physics and the “laws” of magic is that magical “laws” are only principles of correspondences – they can be violated at any time.
Magic can create situations that violate the rules, including the normal rules that magic operates by. Usually, these situations are the result of magic used long ago or by weird, non-human creatures, are the results of misunderstanding invocations, or are due to the influence of powerful supernatural creatures.
There are many who would like to claim that magic is simply a force, neither good nor evil, that is directed as the user desires. Those who have delved into the matter know that this is untrue.
In RCFG, magic is sentient in each of its uses. There is magic that desires to be used, and magic that desires to be forgotten. There are spells that, by their casting, further the aims of the Powers of Good, and others that further the aims of the Powers of Evil.
Not every supernatural effect is strong enough to register as magical. Many creatures may have supernatural abilities, including immunities to certain weapons, that are not strong enough to register as magical to a detect magic spell. Any spell-like ability, though, when invoked, can be detected, countered, and dispelled as though it were a spell.
Living Spells
A living spell is aware of its own existence. It either wants to be cast, or resists being cast. Most living spells want to be cast.
Spells that Wish to be Cast
If a scroll containing a living spell is examined by someone capable of casting the spell, that being must make a Spellcraft check (DC 20 + spell level) or immediately cast the spell.
If the spell is being studied (such as from a spellbook) so as to be memorized, the character must make a Spellcraft check (DC 10 + spell level) or immediately cast the spell.
The character may still attempt to memorize the spell in another, unused, spell slot.
Spells that Resist Casting
If a character attempts to cast a living spell on a scroll, he must make a Spellcraft check (DC 20 + spell level) in order to cast the spell.
If the spell is memorized, the character must make a Spellcraft check (DC 10 + spell level) to cast the spell.
In all of these cases, the Spellcraft check uses a Reaction.
Optional Rule: Spell Misfire
As an option, if a spellcaster struck in combat fails his Concentration check by 10 or more, the GM may rule that the spell was not completely lost – instead it misfired. The spell is still removed from the caster’s spell allotment, but it did something unexpected. Perhaps it targeted the wrong creature. Perhaps it had the opposite effect from what was expected – harming instead of healing, for instance.
If using this option, the GM or player should roll 1d6.
On a roll of “1”, the spell does something unexpected that greatly benefits the caster. For example, it might be cast as though the caster was twice his current level. A fireball might linger in the air, doing additional damage for 1d3 rounds.
On a roll of “2” or “3”, something happens that is neither helpful nor harmful to the caster. For example, grass might sprout from the ground, a second of bone-numbing (but non-damaging) cold might be felt by all, or tiny twinkling lights might appear in the area and remain there for years afterwards.
On a roll of “4” or “5”, something happens that might be harmful to all in the area. For example, twinkling lights appear that cause a –2 penalty for all attack rolls during the next 1d6 rounds, or a pink rhinoceros appears at a random location on the battlefield and attacks the closest creature each round for 1d6 rounds.
On a roll of “6”, something bad happens to the caster. This might mean that the spell targets him. It might mean that damage healed due to a healing spell is taken from his hit point total. The GM should be careful not to make this too damaging, but damaging enough that the die roll is dramatic!
Because of the extra work this option requires, and the extra risk to PC spellcasters, some groups might want to avoid this optional rule. For others, this option aids in keeping magic unpredictable.