Death Night

Once a year, the Witch Elves descend on the streets of their cities in unbridled celebration of their bloody lord -- this is Death Night, a time of terror for all in Naggaroth. The boulevards and alleys echo with manic drumming and shrill pipes, while thick clouds of blood-red incense drift around twisted mansions. Through the smoke prowl roving bands of Witch Elves, murder in their hearts. Under the direction of their Hag Queens they steal away any Dark Elves they find, often breaking into houses to drag the inhabitants to their bloody altars.

It is on Death Night, re-invigorated by the blood of the slain, that the Hag Queens are at their most beautiful and frenetic. Over the course of the following year they slowly revert to their true haggard appearance but, for that one night, they are wanton avatars of lustful slaughter -- true daughters of Khaine.

Source

 * Warhammer Armies: Dark Elves (8th Edition) -- pg. 47