Zarakynel, the Bringer of Torments is the best and (apparently) most beautiful of Slaanesh's creations, but his/her/its model is a six-titted monstrosity, and looks like Shiva had a baby with a daemonette and an albino. He/she/it has fun raping Eldar, especially the exodites, and her favourite delicacy is spirit stones. She is well known as the bringer of torments, the soul-eater, the unholy one, and fucking ugly. She like, quad wields swords and is a complete rape monster. Literally.
At one point, she had a run in with Iskandar Khayon, taking the life of his bitch Nefertari. Before he/she/it could take Nefertari's soul, Khayon used his psychic powers to blast her into the warp. Even though she survived the encounter, it was more than a millennium before she could regain corporeal form. He/she/it vowed to fuck up the goddamn space pansy. One of her most notable appearances is on a planet called Sherilax. A bunch of pleasure cults were having a violent uprise against the planetary governor. The pleasure cults were pleasing Slaanesh greatly, so he/she/it/Hermaphodite/who the fuck even knows sent Zarakynel appeared and converted the Entire planet. It was, in fact, so horrid that even the Inquisition refused to write what really happened there. Oh God.
On the TT
She is an unholy rape monster (literally), dropping to just 460 points in the new edition rather than the previous 666, and is still a Lord of War. She has a 12" move at full wounds, and also inflicts a leadership penalty to any enemy units within 6" of her (both of which decrease as she takes damage.
Her first weapon, the Souleater blade, is S8 AP-4 D3, but to wound rolls of a 4+ deal 3 mortal wounds instead; her second is her slicing claws which are S7 AP-2, deal d6 damage, and get AP-4 on to Wound rolls of 6. Like all Slaanesh daemons, she fights first even if she didn't charge. To get her into combat, she can charge even if she advanced, and once there gets a 3++ rather than her standard 4++.
Like all the uber-daemons, she can be summoned with an "arch-daemonic ritual", where the summoner rolls nine dice to try to reach her power level. Doubles inflict mortal wounds on the summoning character, triples kill them outright (but the ritual can still succeed.) Hey, no one ever said summoning apocalyptic daemons was easy.