The only difference between me and a madman is I'm not mad.
Moving on, I'm gonna start by saying is darkness the best element for insanity. The obvious choice would be entropy but that doesn't feel right. I dunno.
But this is a creative idea, but "would I use it?" is the question. Wouldn't it be more effective/efficient to either kill the creature or antimatter it, opposed to risking your precious creatures to evade damage. But then you can possibly use one creature to wipe out your opponents army. Plus it's a pseudo-lobotomy, which in itself can be good. Yeah, I this is a good kinda non-direct CC which could really work. Does darkness need more denial? Maybe not. Does darkness want more denial? Damn straight.
If you want to fit the darkness theme better, why not go on the "blind" idea? Same effect but more relevant? Just an idea.