The Masque of Slaanesh

The Masque of Slaanesh is the most infamous Daemonette to have ever plagued the sentient creatures of the Galaxy. Once Slaanesh's favoured dancer and chief handmaiden, she was cast out by her master, and cursed to forever dance through Materium and Immaterium alike. The Masque has turned this curse into a potent weapon, forcing any being she manages to seduce with her hypnotic dance to join her performance until it drops dead from exhaustion.

Fall From Grace
During the eternal conflict between the Chaos Gods known as the Great Game, Tzeentch managed to trick Slaanesh into facing against Khorne in combat. For all its might, the Prince of Pleasure could not possibly hope to win against the Blood God, and Slaanesh was defeated and humiliated by its arch-nemesis. Sensing the dark mood of her master, the Masque took it upon herself to lighten Slaanesh's up, and presented herself before her master, performing her most energetic and scintillating dance ever. Alas for the Masque, Slaanesh's humiliation colored all its toughts, and instead of its usual laughter and joy at the sight of the Masque's spectacular dance, the Prince of Pleasure saw only mockery and barbs against its wounded pride in each perfect combination of dancing moves.

Slaanesh's emotions came to a boiling point, and the Prince of Pleasure evacuated its frustrations on its handmaiden, branding her as a traitor, and placing a fell curse upon her, proclaiming that if she so wanted to dance then she must dance forevermore without pause. And so it cames to be that the Masque was forced to dance eternally across space and time, for both mortal and immortal audiences. As she reenacts Slaanesh's greatest conquest and victories, her mask changes to match the roles of the characters she plays, in a manner eerily similar to the way a Harlequin troupe performs. Her curse has brought her to dance for the most improbable of audiences, from taunting the servants of the Blood God at the very doors of Khorne's citadel, to humiliating her former lesser peers amongst Daemonettes. Yet the Masque has turned Slaanesh's curse to her advantage: the lure of her masterful display is so enticing that any who see it is inevitably compelled to join in the performance. Even other Daemons are not exempt from the Masque's enchantments. As her dance goes on, the tempo rises, whith the Masque's unwitting chorus struggling desperately to keep up with her. Ultimately, those enticed by her spell will dance themselves to death, using up their last ounce of strength and dying breath in an attempt to keep pace with her twirls and somersaults.

The Harlequins
As noted before, the Masque's behavior is eerily similar to that of the Eldar Harlequins. This is not altogether surprising, as the Prince of Pleasure was born from the collective depravity of the Eldar race. Enticing Eldars, especially Harlequins, into dancing themselves to death is one of the Masque's favorite activities. The Harlequins have a performance that tells the tale of how the Masque once managed to infiltrate one of their troupes, and entranced both the troupe and the audience with her whirling spell. It was only when a Solitaire appeared that the spell was eventually broken: as the only Eldar able to impersonate "She-Who-Thrists", the Solitaire was immune to the Masque's spell, and was able to match her move for move for six days and nights until the Masque finally faltered and missed a step. Horrified at this failure, the Masque fled, and now seeks eternal revenge on the servants of Cegorach.