I saw something alike to this at one of <PERSON> books, which was I guess on the <PERSON> series.
In the book there was an evil god and one of her servants went beneath the temple and activated the curse of the god.
Affection of the curse is any whom exposed to it goes mad in strange ways. One of the affected was a druid whom had high skilled in the nature art. He turned himself into a bear (which is a high druid spell) and he neither could able to revert into human form nor he was aware of himself. His great powers worked against him.
With this, he attacked his companions, did some violent actions against people who don't deserve it and so. And slowly sucked into madness and violentness.
So after a brief brainstorm you can go with something like this: The beauty of the spell itself convinces people into relentless casters whom takes heed of the magic art as liches or warlocks do...
More so:
When casters cast the spell together they will not affected by the maddening effects. Because they see through each others mind and could see how all the other casters hold on to. But when a person alone perform it, he/she couldn't able to picture/echo which idea is right and which is wrong.
More so person would lose their moral code which they held onto with all of their lives. 805
More they cast this spell alone, more their actions become relentless and more cruel to any who in relationship with this person. And at one point they become someone who do anything to learn more with the nature art. So they expose to unavoidable maddening caused by nature magic art.
ALSO: On DnD (forgotten realms) magic works through the Web of Magic of Mystra. Any spell you cast is exist on the web of magic and struck the target within. Both nature spells, holy spells and arcane and more so, uses the web of magic. This web exist on some other plane... Maybe you can go somewhere from this.
Brainstorm is the feed of art of our world. 227