So, there's a formation listed in the Cypher Dataslate, which is Cypher and 3 units of Fallen. The Fallen use the Chaos Space Marine Chosen rules, but can't have marks or dedicated transports.
I'm planning to make this formation up, because it will look pretty awesome.
I am using Cypher's actual model rather than a kit bash, because I may as well, and he's not that pricey and looks awesome.
I'll use the 32mm bases, once Games Workshop stops being out of stock of them, because that will give the models a good "look" of being a bit bulkier and special.
Model wise, I have a pile of Horus Heresy bits from Forge World from a couple of bits site sales. One Death Guard or Night Lord head in among a normal squad will not look hugely out of place but give them a definite impression of being more unique.
I'll eventually go for the full three squads, with all the plasma guns - this is both effective in combat and fits in well with the Dark Angels relationship with Plasma weapons. It also gives a bit of a nod back to the old Crusade era support squads.
The core of the models will probably be a box of Dark Angels Veterans and a box of Chaos Marines. I want to go pretty light on chaos iconography for the Fallen, as my idea is to make them more "Renegades" than "Chaos Marines".
Paint scheme wise, I want to nod both to the old and new paint schemes for the Dark Angels - I'm thinking of black armour which goes up to a line highlight of Dark Angels Green. I want the green in because I don't want them mistaken for Black Legion or any one of a dozen chapters who use black armour.
Current state of play
Cypher: Undercoated and ready for painting.