Shadow Freddy is a ghostly darkened version of Withered Golden Freddy. His voice should be similarly ghostly, and have a tone of superiority, as if he's planning something at all times. However unlike Withered Goldie, Shadow Freddy should have a bit more ghost to his voice. He is a shadow after all, so he should sound almost like he's barely faded out of existence. He should also still have a bit of glitch like Withered Goldie does. But unlike with Withered Goldie, focus more on the ghostly echo rather than the glitching audio.