Alyson Hannigan, 'Buffy the Vampire Slayer'

Alyson HanniganHow I Met Your Mother (tv program)Buffy the Vampire Slayer (tv program)
Then: Willow started out as the shy, nerdy, lovable witch, but, as shy, nerdy, lovable people tend to do, she went all vengeful villain in Season 6, when her girlfriend was killed and her grief fueled her dark power. You could tell by her hair. Now: Hannigan has never strayed far from TV.... Getty Images/WB
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