Myrdraal are slightly "out of faze" from this world, and this manifests itself through the "making blurs in mirrors, teleporting through shadows, and cloaks not moving." The Dark One isn't a part of the Pattern, he like the Creator are entities outside the Pattern. However, the Dark One has access to the world through the Bore. What I think the price of the True Power might be is this: when you use the True Power you begin to faze out from the world, and the s'aa might appear when you begin "turning into a Myrdraal". Shaidar Haran might be the result of this fazing out. His strange powers come from the True Power, but they are limited, because he is only partly in this world. He can burn spears, and "remove the ability to channel" (I think he just shielded the reborn Forsaken, and Osan'gar just couldn't sense the shield because it was woven of the True Power), but with losing yourself in the emptiness outside the Pattern, you lose options about what you can do with the Power (the Dark One can only lose bubble of evil, not neccessarily controlling how they manifest). I hate to bring him up, but maybe that's what happened to Beidomon. Now, I know that he isn't neccessarily bad, but if he's still alive, then he is bad.