Yet again a secretive kabal of which everyone knows very little! I like the idea of how an archon thinks he has assassinated a foe, just before receiving a letter that tells that he hasn't
...and I think this archon is using more than just a clone-field to stay unknown.
For a list like this, you probably want at least a few kabalite warrior squads. Maybe they could all have different markings, so that you can see which 'cell' they are from?
For dark eldar snipers, I suggest the standard Eldar rangers, they look great and can be painted to be dark too. Since you need an Eldar HQ to bring rangers, Illic Nightspear seems like a good choice for an agent.
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THE KABAL OF LOST HONOUR
THE CULT OF THE BURNING LEAF
THE COVEN OF THE HOLLOWED