How I Met Everyone Else - S3-E5
Other mistake: In the scene where Barney is describing The Vicky Mendoza Diagonal of The Hot-Crazy Scale, his words describe her getting hotter, (i.e. lost ten pounds) not less crazy. On the diagram shown, she goes down in craziness, not up in hotness.
Chosen answer: She was finally shown at the very end of the last episode of season 8, continuing into season 9. The actor's name is Cristin Milioti: http://www.imdb.com/name/nm2129662/.
Knever