On the final day of Games Workshop's Advent Calendar (25 days of pure terror to some), the final release was Cypher, a figure clad in mystery and the most infamous of the Fallen. I couldn't help myself and picked it up.
To begin, with just Cypher - he can be taken in just about any human force, and doesn't take up a force organization chart. Specifically, any army outside of Dark Angels that are human - Chaos Space Marines or other. He is an Infantry (Character), and an Independent Character. His other special rules include And They Shall Know No Fear, Fleet, Hit & Run, and Infiltrate.
He also confers 3 Victory Points to a Dark Angel opponent if killed and "Captured", or 3 VPs to the owning player if he survives. He is captured if there are opponent within D6" when he is killed. If there are no opponents in that range, he escapes and neither side receives the bonus points.
His Profile is generally to be expected for a Space Marine Character, though he is WS7, BS10(!), and I8. He has a special rule that allows him to fire each of his pistols twice in the shooting phase, or run and then fire each once. He has a bolt pistol and plasma pistol which doesn't get hot. He also uses them in combat, with half his attacks rounding up coming from the bolt pistol, with the remainder having a plasma pistol stat line.
When facing Dark Angels, Inner Circle models gain the Zealot special rule. Meanwhile, he cannot serve as the Warlord, and the Warlord of the army he is in suffers a -1 penalty to its Leadership. Finally, his sword confers the Eternal Warrior and Shrouded special rules, but he cannot use it in combat.
The Datasheet also includes a formation for Chaos Space Marines of Cypher and 1-3 units of Chosen. The Chosen cannot take Chaos Rewards, Artifacts, Marks, or Transports. They do gain the Infiltrate special rule, and use Cypher's leadership (10) if they're within 12".
Finally, the book has 6 missions, three Altar of War and three Echoes of War missions.
And, of course, there is a generous selection of fluff. I have not had a chance to read it yet, but I am intrigued by Cypher. At 190 points he's a bit pricey, but he does have some good abilities, even if he is a liability. I don't think we'll see him or his formation in competitive play, but it's definitely an interesting fluffy character.