This comes from someone claiming to have the book in hand, and details out exactly what the Crimson Slaughter is. As a codex supplement we are expecting two pages of rules, as we have seen in previous codex supplements. The rest of the book of course details out the background and history of the Crimson Slaughter.
I know from the past I have enjoyed reading these books, and these rules if true, look like they will be worth taking a good look at.
Please remember that these are rumors, until we get the official release where they can be seen with our own eyes.
via an anonymous source on Faeit 212
Crimson Slaughter
Crimson Slaughter can ally with as Battle Brothers with Chaos Space Marines
All models in the Crimson Slaughter Detachment have Fear.
Choose one unit of chosen to be upgraded at +10pts. Gain preferred enemy.
Possessed are Troops. Roll a d3 at the start of the CS players turn. 1: Unit and Vehicle if embarked are shrouded 2: Unit type becomes Beast 3: Gain a 3+ invul save and rending
Warlord Traits
1. Warlord and unit gain hate, extra bonus's against Dark Angels
2. All enemy units within 12" of warlord suffer a -2 to fear tests
3. Warlord has Rage and Furious Charge, but must charge attempt to assault if within 12"
4. Warlord and unit gain Crusader
5. Enemy models in base contact with Warlord take d6 S3 ap hits at the beginning of each assault phase
6. Warlord has shrouded
Relics
1. Replaces a powermaul on a Dark Apostle S +2 AP4 Concussive and all CS units in 6" gain Zealot
2. Soul Siphon gains powers based off of enemy models removed in close combat. Effects last the rest of the game 1. +1S 3. AP 2 5. +1S 10. Instant Death
3. Furious charge, Hamer of Wrath and rage
4. Gain Divination and can re-roll failed psychic tests. No Deny the Witch bonus's
5. Cannot be taken by a Daemon Prince. Gains 2+ save and it will not die
6. Gain Daemon, Fearless, and fleet, and gains the Crimson Slaughter possessed mutation-roll a d3.