Continuity mistake: Willow's hair changes position between shots when the vampire brushes her hair back and kisses her.
Continuity mistake: Whenever we see the two Willows together in this episode we see that Vampire Willow is understandably very pale in comparison to the living Willow. However, in the library with Cordelia, when Vampire Willow says 'How about dinner?' her face is no longer pale.
Other mistake: In "Doppelgangland", Vampire Willow struggles to remember Cordelia's name. However, it is still Willow, she knew Cordelia from being human (we see this in The Wish as well).
Revealing mistake: Near the end when the good Willow says goodbye to the evil Willow and hugs her, there is a shot of the back of the good Willow's head and the evil Willow's face. You can tell that the good Willow is a body double wearing a wig - there's something circular near her scalp, possibly an elastic band.
Revealing mistake: Right at the beginning of the episode, Buffy is sat outside with Willow and Willow is levitating a pencil. The pencil is obviously CGI as it stands out from the rest of the picture and doesn't cast a shadow. It also disappears from view whenever there is a side-angle shot of Willow.
Revealing mistake: Both the good and evil Willows' faces are barely seen onscreen at the same time due to them being played by the same actress, but when they occasionally are the good Willow stands out from the picture more than the evil Willow. She must have been filmed separately from the good Willow and edited in later.
Revealing mistake: When evil Willow licks good Willow's neck the neck that you see is a lot longer than either of theirs. Since both Willows' faces cannot be filmed at the same time a body double must have been used for this shot.
Answer: She has superpowers, ergo fast movement. The reason she outruns him so easily in "Touched" is that she stops trying to actually fight him and just dodges instead.
Shay