A little while ago, I stumbled upon this. I didn’t know Mike fancied the world of Athas.
He also gave a small update! https://twitter.com/mikemearls/status/934577791680389120
Neat and simple. Doesn’t it however give too much power to spellcasters, especially those with lucky rolls? And understandably, defiling can be dangerous while within a city, but who cares when you’re travelling in the middle of nowhere, or exploring ancient ruins?
I have a group that spends a significant time outdoors, none of them plays any good characters, and most of the random combat encounters occur during their travels (it’s one harsh setting, we all know), so it comes naturally for one to defile and empower their magic while the others turn a blind eye. It just so happens that the players are excellent RPers and they play their part of despising defiling magic, so defilers in the group (so far, only one) go to great lengths to hide their abilities, for fear of being exposed and subsequently, hunted down.
Just increase the odds. 15+ works ok for me. Lorewise, defiling is a stronger way of casting (you’re dopping yourself with life force to make your magic “easier”), so I see logical that you can use magic without expending your spell slot if you can expend another source of energy.
It also easily applicable to all 5e spellcaster classes, and that is a plus.
I actually REALLY like this solution. It makes it accessible to everyone, and it’s a simple and elegant rule.
What zontoxira says is more a feature than a bug: you DO have examples of traveling spell casters who defile in the wilderness while their companions turns blind eye: look at elf tribes and raiders. Sadira’s whole experience in the 2nd PP book, for example.
And that “who cares?” mentality is EXACTLY why Athas is such a crap-sack world.