Battle of wills

I keep meaning to expound more on the topics of character classes in my fantasy heartbreaker, and on campaigning with micro-settings, but sometimes a new idea pops into my head that's just too intriguing (to me, at least) to wait.

One thing about the D&D magic system that's always bothered me a little is the standard saving throw.  Unless an effect causes direct harm through hit points of damage, it's usually a starkly binary outcome: Fail the save and the spell has full effect; make the save and the spell has no effect at all.  That means that a spell-caster takes a huge risk in casting a non-damaging spell, especially if it's at a single target, because if the target makes its save, the spell is simply wasted.  And since saving throws depend entirely on the level or HD of the target, and usually not at all on the skill of the caster, even a high-level wizard is hesitant to use a big-ticket spell on a particularly formidable opponent (and at the same time, reluctant to waste potent magic on a low-level pushover.) 

Most of the time, in fantasy fiction, a hero doesn't just fall under a spell instantly, nor does he just shrug it off.  There's almost always a great battle of wills between the hero and the villainous wizard or priest.  Sometimes it's shown as a battle inside the would-be victim's head; others, it's depicted outwardly with alternating shots of hero's and villain's faces grimacing with the tremendous effort of overpowering the other.

Hmm...overpowering.  Thinking of it in those terms reminded me of the grappling system I cooked up for G&G.  It's essentially one character trying to overpower another, except mentally/spiritually/magically rather than physically.

Here's the idea:

Whether the saving throw is made or failed, unless with a natural 20 or 1, respectively, a spell can result in a battle of wills between caster and target. 

If a save is failed, then the target may continue to resist, and if the save is made, the caster can continue to force the spell on the target.  The "loser" of the initial save must overpower the winner for a number of rounds equal to the difference between the number needed to save and the actual result of the roll. 

For instance, if Monfort the magician casts a charm spell at Wilfred the warrior, and Wilfred needs a 12 to save but rolls a 9, Wilfred may still fend off the charm if he can resist Monfort for three rounds in a battle of wills.  If Wilfred made his save with a 16, Monfort could still force the effect into Wilfred's mind by overpowering him four rounds in a row.

Each rolls 1d6.  The caster adds the adjustment for his or her Presence ability score (Charisma for standard D&D) and half his or her level of experience.  The target adds its adjustment for Wit (use Int or Wis in D&D) and either its level (for spell casters) or half its level (for non-spell-casters, rounded down.)  High total wins.

If you like, use the target's Might (Strength or Constitution) for spells which affect the physical body, like polymorphs.   For monsters, use half the creature's Hit Dice plus whatever adjustment you deem suitable for its mental strength, or just its full HD for body-affecting spells. 

Also if you like, the target may take damage when losing a roll, either psychic/subdual damage or real physical damage, depending on the nature of the spell, at a rate of 1 point per point of difference in the magical overpowering rolls. 

During each round of struggle, the caster and the target are limited in their actions.  The caster must maintain concentration, may move at only half speed, and cannot attack or cast other spells.  The target may move at half speed and engage in combat if it wins the round's overpowering roll, but at a -4 penalty to its combat rolls (or attack rolls, for D&D.)  The caster may abandon the spell at any time.  The target may likewise give in and allow the spell to take effect, which is a viable option if damage is inflicted on a failed roll. 

If the caster's concentration is disturbed, such as by an attacker making a successful combat roll, the target automatically wins the round.  If the caster is targeted by another spell, he or she may abandoned the overpowering attempt to defend against the other spell, or may maintain it while defending, but adding only half level to the 1d6 rolls.

This is all sort of hastily cobbled together, so of course feel free to point out fatal flaws or suggest tweaks or revisions.