Roman said:
Magic functions as a ripple in the calm surface of reality. The magical field of the world can be thought of as a series of interconnected puddles, pools, lakes, seas and oceans of magic connected with streams and rivers of magical energy.
Casting a spell disturbes the surface and creates ripples spreading outward. Depending on the strength of the spell, these can be detected by mages and other magically attuned creatures at a distance. Casting too many, too powerful spells too quickly in succession, can, depending on the size of the local pool, exceed the capacity of the pool to absorb these ripples and thus can result in the failure of the spells and/or unintended magical effects.
Hmmm... let me think about this.
Perhaps it's worth borrowing some mechanics from WFRP for this. In WFRP, you can theoretically cast spells as often as you want, but you have to rull a number of d10s and add them together to reach a so-called "casting number" - the spell only succeeds if the number is reached.
Furthermore, each time you roll multiple numbers with these d10s (for example, if you roll "5" two times), Something Bad happens. The spell still goes off, but you have to deal with some nasty side effects. These range from "your hair stands up for 1d10 minutes" for doubles to "you are sucked into a parallel dimension and die screaming" as the nastiest result for quadruples.
Now, how can we use this for D&D? Well, let's say arcane magic works like this:
You don't have to keep track of spell slots and don't have to memorize spells. You can attempt to cast a spell as often as you want. However, each time you want to cast a spell, you have to make a Spellcraft roll.
The base DC is equal to 10 + (spell level)x5. You
can Take 10 on this if you are not rushed and outside of combat.
The DC will be modified by the number and level of spells that have been cast "recently" and "in the same area". Add the highest spell level that has been cast to the DC, as well as +1 for each additional spell that has been cast at this location.
"Recently" is an amount of time that depends on the spell level. The effects of a 1st level spell probably shouldn't linger for more than an hour, while the effects of a 9th level spell should linger for days, if not weeks.
"In the same area" likewise depends on the spell level. For a 1st level spell, this would perhaps be 10 meters. For a 9th level spell, we are probably talking about dozens of miles.
Additional effects - such as being in the Dark Zones, or close to magical artifacts that calm the local magical field - can also modify the DC.
If you fail the Spellcraft roll by 5 or less, you have to roll two dice. If they come up as doubles, you will have to roll on a "Side-Effect table" to see what happens. If you fail by 6-10 points, you have to roll
three dice. If you roll doubles, you have to roll on the same table, but if you roll
triples, you will have to roll on a table with more severe side effects. And so on - for each 5 points by which you fail, you will have to roll another dice, and for each additional multiple you get, the side-effects will be more severe.
This system would be another way of balancing arcane magic (though it shouldn't affect divine magic - divine magic comes directly from otherworldly entities). However, I'm not sure if this isn't too much bookkeeping to keep track of where what amount of spells has been cast. Furthermore, this system has not been playtested, so it's hard to say how well it would work in general practice.
