Daruna - Corruptive Magic

Wow. This place is dusty. Guess I need to break out the vacuum.
I'm finally doing some work on my Daruna campaign again. We're scheduled to play the first session in a few weeks. One aspect of this game is a bit of swords and sorcery feel, with powerful magic a tool of the big bad guys rather than the player characters. To reflect this I've been working on a system of magical corruption. The how and why follow...

World View

• Magic is damaged / corrupted.
• Weak magic is accepted / useful.
• Potent magic is a bargain with the devil, leading to madness, destruction, or worse.

Desired Effect

• High level magic is effectively not an option for players.
• Use of low level magic is relatively safe, but not 100% reliable.
• Higher level magic is cumulatively more dangerous or less reliable.
• Corruption is a bad thing and very difficult to reverse once started.
• A mechanic that reflects the continuum of corruption.

Mechanic
The base mechanic involves two things, corruption points, and corruption effects. Corruption points are a cumulative measure of magical corruption, corruption effects are the visible or invisible changes to the character caused by corruption. How do you get these points and effects? Like so:
Spell casting requires a successful save vs. X (X determined by spell sphere).

• Success: spell works normally.
• Failure: either spell fails or caster forces success and gains corruption equal to spell level. Failed spells are simply a lost action. All spell resources retained.
• Critical Failure: A natural 1 or failure by 10+ applies a long term corruption effect. The greater the accumulated corruption, the greater the effect. A character with zero corruption points never suffers a corruption effect.

The save DC is based on spell level: X + (Level^{^2}). The tentative X = 5. Save DC goes up FAST. The DC for a 4th level spell is 21 (X = 5).
Of course corruption points provide benefits to those that embrace them. Corruption can be used to enhance magic, but using corruption... earns more corruption!

Net Effects
Characters who wish to avoid corruption face occasional spell failure, but failure is similar to a combat fumble in effect, a lost action. Powerful magic becomes a dangerous option, but players retain control of their character's fate, which is very important. Players also face potentially interesting choices in critical situations: force the failed spell to work and take a point of corruption or let a friend die?
That said, once a character that starts down the path of corruption he or she is going to fall to its effects. There's no turning back without a supreme effort. Like a multi-session quest / geas. Characters that fall under the sway of corruption eventually become NPCs.
So why make it so complicated? From the player perspective, it's not really that complex. Cast a spell, roll a save. Spell fails if you fail the save. Done. From my perspective, it's a tool providing access to a spectrum of interesting NPCs and villains and a model for a key element of the larger campaign picture.
We'll be testing this in our first game session and see how it goes. Since we're using my Class Free rules, this and many other aspects of the game are up for discussion as play continues.

Addendum
As to why this site has been so empty, I pretty much haven't been doing anything gaming related over the summer, or at least nothing interesting enough to inspire an article. Our gaming group was on hiatus for various reasons, and my video gaming was mostly Eve, which I've gotten a bit bored with lately. With the Daruna game starting up at least I'll have something to scribble about now.