Another mention of this オギプルギスの夜 (Ogi Puru Gisu no Yoru) thing. It's linked with something called 魔法小木 おぎか☆オギダ, or Mahou Shouki Ogika☆Ogida. The video on Nico Nico has now been removed to a copyright complaint from TBS, but there's another video about the "aftermath" of it. Ogi is the name of one of the two hosts, it seems.
Ah, the "Puru Gisu" was the "purgis" of "Walpurgis"! I feel silly for not realising. I thought the "no yoru"/"night" at the end was referring to the podcast, like an evening show (e.g. "Rock Night with DJ Danbooru"). Doh.
@Deacon: I'd say so, since she's also acting like her and the implication is that she's forgotten her character and has become Senjougahara.
