Nymphadora Tonks
Nymphadora Tonks is a face-stealer, and she steals them utterly and completely, every detail raided and pirated, the colors and the scars and all the facets of voice. Ten million faces and it is easy, she's too good at it and I swear, Professor, Auror Academy will be a cinch and it scares the hell out of her sometimes, how complacent she's grown with it.
Mostly, it scares her how it might go wrong when she's attempting the tricky whole-body transformations, like splinching, and she's suddenly caught in the in-between of two identities and they wouldn't pair well, like veins crisscrossing into a labyrinth, or blood types that don't match, two halves of a a heart that wouldn't fit together.
On rare occassions, though, it scares her even more that she might steal their minds and souls along, in a fit of desperation or recklessness or the awful Black madness that runs through her blood, and her own would be lost somewhere in the void.