I've only ever seen the 4th edition Chaos Codex, and I've seen so many complaints about Possessed. I've been thinking and I'm going to try some 'modification.'
Possessed Chaos Space Marines
Cost: 20 points each. Statline and options are the same as normal, as well as:
Daemonic Gifts All Possessed have Daemonic Protection (5+ Inv save) and Daemon Strength (S5). For the following points cost, any number of Possessed may be given any number of gifts.
Daemonic Fire: The model counts as having a Flamer. 5 points per model. Maximum of 2 models can have this Gift.
Daemonic Blades: The model counts as having a power weapon. 10 points per model.
Daemonic Talons: The model's attacks are Rending. 5 points per model.
Daemonic Hooves:The unit has Fleet. 3 points per model, must be taken on all models. Daemonic Speed:The unit has the Scout rule. 4 points per model, must be taken on all models. Daemonic Resilience: The model has Feel No Pain. 7 points per model.
Daemonic Bloodlust: The unit has Furious Charge, but also gains the Rage rule. 2 points per model, must be taken on all models.
Daemonic Power: A Possessed Champion may become a psyker for +20 points, so long as the squad has no Icon of Khorne, and may select one psychic power from the Codex (god-specific powers require the relevant Icon), at the full cost of that power (always round decimals up). If the squad has an Icon of Tzeentch, an extra power may be taken at half the cost of that power.
Probably needs some work. I'd also like some suggestions for more gifts. I do a lot of narrative stuff, so I really like doing this sort of thing for Arena of Death and the like.