The only real "complaint" I have is that I wish that for the 4 gods list would have "All units in this formation gain the Mark of ____ for free" - not too OP I think.
The problem with the Marks is that it's a cost per model. Depending on the number of squads and models in them, as far as the size of the battle, such advantage could reach hundreds of points.
I would rather leave this open until we may gather other advises.
Also I think you should just make it 1-6 troops (since currently the cult units become troops with the appropriate HQ) and just state that there must be at least 1 squad of Noise Marines/TSons/Zerkers/Plague marines.
This eases up the Troops entry of the force organisation, for sure, and allow larger MSU with cultists.
Then, it comes back to something closer to a CAD : 2-6 Troops (one of them being a Cult Marine one).
For the Slaanesh one - why not state that every vehicle gains a Dirge Caster + the ability to swap a heavy weapon - helps with units that do not have heavy weapon - aka rhinos.
In matter of points, it would not represent too much (for 10 vehicles, which would already be a lot, dirge casters only cost 50 points).
I like the idea. I just make an "or" condition for it, as Blastmasters upon vehicles is something that just doesn't exist (anymore) in the codex. A rhino would get a Dirge Caster for free, another tank could have both for 5 points, a Helbrute or Daemonforge engine would have to make a choice between them (as they can't be fitted with Chaos Vehicle Equipment by default).
"Children of the Warp"
Why not just let the possessed just choose which power they want, instead of a re-roll?
I would love too, as Possessed are the core unit of my Word Bearers army
But some things have to be considered, IMHO :
- "Daemon" is a very powerful trait for Space Marines (5+ invul save, plus their basic 3+ armour save, that can be boosted by Psychic Powers or Daemonic Rewards, and ... Fear, which is globally not very useful until it takes effect) ... it also allows CSM Sorcerers to use Malefic Daemonology without perils on all doubles with the Crimson Slaughter "Prophet of the Voices" relic,
- Chaos Daemons Codex is the most "random" one (Warp Storm table, effects of Exalted Rewards, Daemonic Instability, ...). Therefore, it seems strange to remove the dice for a "Daemonic table" (and I don't see other units able to choose a specific boon from a table each turn),
- When we look where Possessed come from, the current Codex already made them better than they were (3 random boons instead of 6, with more specialized effects), and that has been improved with the Crimson Slaughter "Slaves to the Voices" table.
Shortly speaking, I think that rerolling a 1/3 chance to get the best effect is already a significant boost.
By the way, the "Daemonic Pact" Detachment (which would be the most suited Primary Detachment to a "Children of the Warp" Formation) allows to field up units of Daemon Chosen (compared to the Possessed : no S5, no random table, but the possibility to equip them with AP weapons, bikes or jump packs and no Initiative loss when charging through cover due to offensive grenades).
Just grant Demonic possession to the vehicles; I would drop Siege Crawler from the list of USRs granted.
State that CSM models cannot take a Mark.
I just "blindly" gave all vehicles all the traits from each of them. But "Siege Crawler" seems weird, actually (moving Tanks as Beasts seems odd). Even the "Crusader" trait seems odd, as non-Walkers do not Run and do not make Sweeping advances either.
So, this formation would be an advantage for the number of vehicles available, and would "just" give the Daemon and Daemonforge traits to Tanks.
For the Mark, I'm not sure. Is it because it would make Chosen too powerful (given Squire example above) or because the Dark Mechanicum is, fluffy speaking, never dedicated to a specific God ?
In the former case, the question is "Is it too OP (with the Mark of Nurgle and bikes) ?"
In the latter case, it depends on the Dark Mechanicum fluff, IMHO.
No Traitor Guard Formations?
No, because Traitor Guard is not present into the current CSM Codex (and also because I do not know them at all ... yet).
One of the ways to give Chaos more diversity and identity would to make FW Traitor Guard Codex into an official GW one (with CSM as Battle Brothers, like Daemons are).
Edit: I really like these BTW, just a couple of minor things that I would certainly change.
Show some more?
I don't have more Detachments/Formations in stock. I think those are covering all the aspects of CSM that I have seen in W40K sources.
By the way, I'm quite open to a collective brainstorming in order to improve the base and transform it from an individual to a team work ;)
PS : document modified (Cult Formations, Insane Melody Formation and Dark Mechanicum Formation)