03E16 - Doppelgangland

Anyanka, the demon who used her power to grant wishes to let Cordelia unwillingly create a world without Buffy as Sunnydale slayer, failed since then to get top-rank demon D'Hoffryn to rehabilitate her, but finally gets a chance to succeed in her menial incarnation as Sunnydale High pupil Anya: Willow, who is frustrated as a girl and individual, always taken for granted, in Buffy's shadow and just got railroaded by principal Snyder to 'tutor', or in fact slavishly do the paper writing on her own, for a spoiled jock brat, hunky Percy West, who even explicitly barks at her as his menial flunky, naively accepts to help 'Anya' with a black magic spell. Willow realizes only too late she's really working for the wrong side, stops before Anyanka's power-amulet is revalidated, but still summons a parallel Willow from a black dimension where she's a master vampire, who now makes her grand entry in Drusilla-style at the Bronze, co-existing with gentle Willow. The gang has no time to mourn 'the best of us', who urgently must join in again with Angel, while the new official Watcher, Wesley Wyndam-Pryce from England, proves of little use, to survive and get rid of the dark 'alien' version, while both go undercover as the other...