Walpurgisnacht
A folk belief holds that in the night between April 30 and May 1, upon the boulders in the Harz mountains, the witches meet in celebration with the devil. The celebration is a Bacchanalia of the evil and demonic powers.
At this festival, Mephistopheles draws Faust from the plane of love to the sexual plane, to distract him from Gretchen's fate. Mephistopheles is costumed here as a Junker and with cloven hooves. Mephistopheles lures Faust into the arms of a naked young witch, but he is distracted by the sight of Medusa, who appears to him in "his lov'd one's image": a "lone child, pale and fair", resembling "sweet Gretchen".
http://en.wikipedia.org/wiki/Walpurgis_Night
https://en.wikipedia.org/wiki/Faust:_The_First_Part_of_the_Tragedy