Looking at the new CSM rumors, I think there are actually some very solid new possibilities for the Heretic Astartes, which makes me quite happy from a gaming perspective. We will have to see how things actually work out in the long run, but the access to “Hatred: Imperium” and free VOTLW for all units in the Black Crusade detachment is a solid boost which should at least put CSM in the picture from a competitive perspective, especially with all CSM basically being Ld10 (as long as their mandatory Champion is alive, that is).
More specifically, I think the following formations will integrate quite well into a competitive CSM army, whether they are actually part of a Black Crusade detachment or not —
 FAVORED OF CHAOS – With a Daemon Prince and 3-5 units of Possessed, I think this formation actually has tremendous potential, despite the bad rap that Possessed currently have in the game. As long as the Possessed are within 12” of the DP from this formation, then they automatically get ALL THREE mutations from the Mutation Table each turn, which takes them from a mediocre, somewhat overpriced unit to one of the top melee units, point-for-point, in the game, almost rivaling Wulfen or Death Company.
For example, if the Possessed from this formation have Mark of Khorne and the Icon of Wrath, then on the charge they each have 5 x S6 AP3 attacks, all at I5 and with re-rolls to Wound. On top of this, if they are part of a Black Crusade detachment and are fighting against any of the Imperium armies (which is quite a good possibility, given the current meta these days), then they get re-rolls to Hit from Hatred as well. Throw in their 5++, Fearless, and Fleet and you have quite a potent self-contained assault unit. A squad of 5 Possessed like this coming out of a Land Raider would have 25 x S6 AP3 attacks on the charge, with re-rolls both to Hit and to Wound… against a standard T4 opponent, that is 18 hits, about 17-18 wounds, and 17-18 Unsaved Wounds against anything with a 3+ save or worse (even against TEQs, that is still about 3 Unsaved Wounds, which is quite solid for a 5 man unit).
A unit of Possessed can even handle some of the tougher GMCs, like a Stormsurge or Wraithknight… with 25 attacks, about 16-17 hits, about 12 AP3 wounds, and about 8 Unsaved Wounds after FNP rolls, a minimum squad of 5 Possessed can “one shot” a Stormsurge with relative ease in close combat… similarly, against a Wraithknight, a squad of 10 Possessed has 50 attacks, 25 hits, about 8 wounds (thanks to re-rolls to Wound), and 5-6 Unsaved Wounds after FNP rolls, which is quite solid for dealing with this dangerous GMC.
Aside from how effective (and reliable) Possessed become when they automatically get all three mutations, a properly kitted out Daemon Prince is nothing to sneeze at and he can work in conjunction with the rest of this formation (or the rest of your CSM force as a whole) to apply very significant pressure to the rest of the enemy force as required. For example, a Nurgle DP with the Wings, Black Mace relic, PML(3), and multiple rolls on Biomancy is very dangerous, especially if he gets Iron Arm for T8 and/or Endurance for EW/FNP(4+), which combine with his ability to get a 2+ Jink save to make him nearly impossible to bring down for many armies. The biggest challenge in this case is having the Possessed Marines keep up with a Winged Daemon Prince, basically require an expensive investment in multiple Land Raiders.
 THE LOST AND THE DAMNED – Consisting of 1 Dark Apostle and 4-9 squads of Cultists, I think this formation is another definite winner for competitive CSM players. For special rules, the Dark Apostle gives Zealot to all Cultists units within 6” of him, which makes them tremendously effective for holding objective and/or serving as “tar pit” units for dangerous enemy units, if you can get the Cultists into combat with them. On top of this, the formation has the “Tide of Traitors” special rule which, every time a unit of Cultists is completely destroyed, allows you to roll a dice and, on a 4+, put an identical unit of Cultists into Ongoing Reserves, with the bonus of having the Outflank special rule as well.
Just from pure utility of grabbing objectives and absorbing enemy combat power away from the rest of your force, I think the Lost and the Damned formation is an excellent option for CSM on level with other cheap, “cannon fodder” type units like Gretchin, Gaunts, Plague Zombies, Conscripts, Kroot, etc., especially with the ability to be Fearless and to “regenerate” themselves after being destroyed. With the “minimum” load-out for this formation only costing 61 MBs, you can take it as a CORE choice for the Black Crusade detachment or as an ally to your existing army with plenty of points left over to spend on more specialized/capable units.
I think this formation can be especially effective when combined with the “Hellforged Warpack” formation with a Warpsmith and 3-5 Maulerfiends, since it can put your opponent on the horns of a dilemma: if they attempt to destroy the Maulerfiends, then that leaves the Cultists free to flood across the board, take objectives, and/or tie up enemy units in assault. On the other hand, if your opponent focuses on the Cultists, then that leaves the Maulerfiends free to displace 13-18” turn 1, then set up a charge on turn 2-3, which can be highly effective against any enemy force which doesn’t have a strong melee capability of its own.
 CULT OF DESTRUCTION – Another very solid new formation, the Cult of Destruction is made up of 1-3 Warpsmiths and 3-5 Obliterator/Mutilator squads (any combination). The formation special rules basically allow each Warpsmith taken to double the shooting attacks of a single Obliterator squad or double the close combat attacks of a single Mutilator squad each turn (they must switch weapons for each set of attacks, though, and also cannot use the same weapons as they used the previous turn. I think the way this formation will be used most commonly is to take 3 Warpsmiths and 3 Obliterator squads, all with the Mark of Nurgle… attach a Warpsmith to each Obliterator squad, then proceed to have them “double-tap” each turn as they relentlessly advance up the board.
Taken all together, that is A LOT of highly durable, powerful shooting available as a mobile “firebase” for CSM players each turn. This formation can also combine well with the “Lost and the Damned” formation discussed above, I think, since the Cultists can provide a mobile “meat shield” for the Obliterators while they advance, while the Oblits in turn provide very significant fire support to your Cultists specifically and the entire army as a whole. Here is how I would pair up weapons, based on the specific target, for the “double-tap” ability the Obliterators have:
- Light-Medium Infantry (long-range) – Plasma Cannon followed by Assault Cannon
- Light-Medium Infantry (close-range) – Heavy Flamer followed by TLed Flamer
- Heavy Infantry/MCs – Plasma Cannon followed by TLed Plasma Gun
- Vehicles (long-range) – Lascannon followed by Assault Cannon
- Vehicles (close-range) – Multi-Melta followed by TLed Meltagun