Battle of Biel-tan
During the Thirteenth Black Crusade a new sect of Eldar known as the Ynnari emerged. Led by Yvraine, they sought to resurrect the God Ynnead without having to sacrifice the Eldar race. The Ruinous Powers were alarmed by this development and sought to foil the rebirth of Ynnead at all costs. They key to the Ynnari's plans were the recovery of the Crone Swords, several of which were on Craftworld Biel-tan. Thus both the Ynnari and Chaos forces sought entry into the Craftworld.
A Webway portal onto Biel-tan was discovered by the Forces of Chaos on the Maiden World of Ursulia, and it is here that they made their move. A massive Warp Storm ravaged the Maiden World, decimating its population of Exodites before The Masque and Skarbrand lead an invasion of Slaaneshi and Khornate Daemons. Skarbrand cares little for his allies and initially tries to slay The Masque, but she is able to convince the Bloodthirster into a temporary alliance. Biel-tan, oblivious of the Chaos plans, nonetheless sends a sizable expedition to Ursulia in order to defend one of the precious Maiden Worlds of the Eldar. The counterattack is led by Autarch Meliniel and a massive battle erupts on Ursulia's surface. The Masque eventually discovers Ursulia's Webway Portal and has Skarbrand destroy its protective wards. With the way to Biel-tan open the Daemons enter the Webway.
Knowing of the incoming Daemonic threat, Biel-tan seals most of its portals but The Masque is able to nonetheless infiltrate the Craftworld. She hypnotizes all Eldar that come before her, allowing them to become vessels for Daemonettes. The quiet Chaos infiltration ends when Skarbrand and his Khornate legions smash through Biel-tan's main gate and a vicious battle erupts. Biel-tans Avatar is awoken and clashes with Skarbrand personally while Jain Zar and a force of Howling Banshees attempt to subdue The Masque before she can summon even more Daemons. Despite Jain-Zar besting the Masque, the Daemon is able to enter Biel-tan's Infinity Circuit and begins her attempts to destroy the Craftworlds very soul.
It was at this point the Ynnari, led by Eldrad Ulthran and Yvraine, arrive at Biel-tan. Consisting primarily of Harlequins and Dark Eldar followers, the Ynnari are able to turn the tide of the battle. Skarbrand and his hordes are destroyed or forced back into the Webway. As the Daemons are mopped up Yvraine is able to save Biel-tan's Infinity Circuit from The Masque by creating Yncarne, though a great many souls are sacrificed in the ritual.
- 1: Gathering Storm: Fracture of Biel-Tan, Part 1
- 2: Codex: Craftworlds (8th Edition) — Eldrad Ulthran