If your Army Faction is GENESTEALER CULTS, you start the battle with a number of Resurgence points, depending on the battle size, as shown below.
Each time a unit from your army is destroyed, if every model in that unit has this ability, you can spend the relevant number of Resurgence points shown below based on that unit’s Starting Strength.
Aberrants. For 5 models, you must spend 4 Resurgence points. For 10 models, you must spend 8 Resurgence points. Acolyte Hybrids with Autopistols, or Acolyte Hybrids with Hand Flamers, or Hybrid Metamorphs. For 5 models, you must spend 2 Resurgence points. For 10 models, you must spend 4 Resurgence points. Atalan Jackals. For 5 models, you must spend 2 Resurgence points. For 10 models, you must spend 6 Resurgence points. Neophyte Hybrids. For 10 models, you must spend 3 Resurgence points. For 20 models, you must spend 6 Resurgence points. Purestrain Genestealers. For 5 models, you must spend 2 Resurgence points. For 10 models, you must spend 6 Resurgence points.
If you do:
Cult Ambush is a type of Strategic Reserves. Units in Cult Ambush cannot be targeted with the Rapid Ingress Stratagem, but can be set up on the battlefield using a Cult Ambush marker as described below, or by following the rules for Strategic Reserves in a subsequent turn.
Use a circular 32mm diameter marker for Cult Ambush markers. If an enemy model (excluding AIRCRAFT) ends any kind of move within 9" of a Cult Ambush marker you placed, that Cult Ambush marker is removed from the battlefield. At the end of the Reinforcements step of your opponent’s next Movement phase, for each of your Cult Ambush markers still on the battlefield, you can select one unit from your army that is in Cult Ambush and set up that unit using that Cult Ambush marker. To do so, set that unit up on the battlefield more than 9" horizontally away from all enemy units, with at least one model in that unit touching that Cult Ambush marker and all other models placed wholly within 3" of that Cult Ambush marker (that Cult Ambush marker is then removed from the battlefield).