Take large Neophyte Hybrids blocks, because they are the only unit both detachments name, and because they are the cheapest thing in the faction to bring back: 3 Resurgence points for ten models, 6 for twenty.
Lead them with a Magus, Primus or Acolyte Iconward. Those three are the only models that unlock Xenocreed Congregation's Feel No Pain clause and the only legal carriers of all four of its enhancements. The Primus is worth a second look: its Cult Demagogue ability was rewritten in this pack to add 1 to the Hit roll for every model in the unit it leads, which stacks directly with Xenocult Masses' Fanatical Hail re-rolls.
Stand in terrain deliberately, and stand in it completely. Two of Xenocult Masses' three stratagems have terrain conditions, and Slunk from the Underbelly requires every model in the unit to be inside the terrain area. One model hanging out turns it off.
Keep The Downtrodden Rise in reserve. It costs 2 CP and it is Xenocreed Congregation's escape hatch from the whole marker economy: a hybrid unit in Cult Ambush can be set up without a marker, more than 6 inches from all enemy units. Against an opponent who has spent the game walking cheap units at your markers to delete them, that stratagem is the answer, and neither of these two detachments has a marker-saving tool otherwise.
What this army cannot do. It has no answer to armour. Nothing in either detachment improves anti-tank output, and hybrid infantry with autoguns will not remove a heavy vehicle no matter how many re-rolls you stack. If your local meta is full of tanks, Brood Brothers Auxilia or Biosanctic Broodsurge, whose Gene-twisted Muscle adds 1 to Wound rolls against Monsters and Vehicles, are the better second detachment.
Buying it. Combat Patrol: Genestealer Cults is the entry purchase and Battleforce: Genestealer Cults the larger bundle; check the box pages for current contents and price. Our catalog holds no Genestealer Cults single-unit box, so we link none for the individual models above.