When Dresden was using his Sight on Victor Sells home he changed.... Here is a glimpse of it:
"I prepared to destroy the lake house, the Shadowman, and any of the pathetic underlings he had with him. With such power, I could cast my defiance at the Council itself, the gathering of white-bearded old fools without foresight, without imagination, without vision. The Council, and that pathetic watchdog, Morgan, had no idea of the true depths of my strength. The energy was all there, gleeful within my anger, ready to reach out and reduce to ashes all that I hated and feared."
Someone (his mom?) intervened and snapped Harry from this. I believed that this was either Harry's own taint from the black magic he'd used in the past, or the corruption of the place. However now I'm wondering if it was Nemesis... Nemesis doesn't seem to force people to do things, but to use their own feelings, and twisting the person into wanting to act a certain way. Also part of Harry snapping out of it was him saying his full Name similarly to how he used it against Before.