As I study the new Cult Mechanicus book, one of the formations that jump out at me is the Cohort Cybernetica. For those who are not familiar with it, it consists of (1) Tech-Priest Dominus and (2) Kastelan Robot Maniples, all grouped into a single unit (which the Dominus cannot leave).
In practice, this means you have a minimum of one Dominus, two Data-Smiths, and four Kastelan Robots, with the option for up to four more Datasmiths and eight more Robots, though that becomes ridiculously expensive very quickly.
In terms of Special Rules, as long as the Dominus is alive he allows the Kastelan Robots to change their Protocals instantly at the end of your turn (rather than waiting until the start of your next turn for the change to take effect) and every Dominus/Data-Smith in the unit can sacrifice its shooting to allow a single Kastelan Robot to shoot a different target than the rest of the unit. Finally, the whole unit yields (3) Victory points if it is completely destroyed (which is quite difficult to do) and also counts as three units for the purposes of calculating Canticles of the Omnissiah.
So, how to use this unique formation? First of all, I recommend having all the Kastelan Robots replace their Incedine Combustors (i.e. Torrent Flamers) with Heavy Phosphor Blasters. Not only do these have 36″ range, S6 AP3, and 3 shots a piece, but they also have the Luminagen rule, potentially serving as “quasi-Makerlights” if they inflict an unsaved wounds/glance/penetrating hit). While the Torrent flamers are nice, I think the Heavy Phosphor Blasters are much more versatile (they can even be used against light vehicles in a pinch) and force multiply the rest of your army as well.
Shooting aside, where the Kastelan Robots really shine is in close combat with the Conqueror Protocol activated (this doubles their base Attacks, but at the cost of not being able to shoot at all). This means that, with Conqueror Protocal on, each Kastelan Robot has T7, 3W, a 3+ save, and 6 x S10 AP2 attacks on the charge, all at I2 (so still slow to strike, but importantly striking before any enemy PFs, THs, or other Unwieldy weapons). Using the Cohort Cybernetica, with its minimum of four Kastelan Robots, that’s 24 x S10 AP2 attacks on the charge, plus another 6 x S8 AP2 Unwieldy attacks from the attached Datasmiths and another 4 x S5 AP2 Power Axe attacks from the attached Dominus. Given that the entire unit is Fearless and goes with majority T7 (at least until two of the Kastelan Robots are killed), this is a brutal formation in close combat which can threaten any and everything it gets close enough to assault.
The difficulty, of course, is getting this formation of Monstrous Creatures and attached characters close enough to the enemy to get into combat to begin with. Since it can only move 6″ a turn, cannot ride in vehicles, cannot DS, and cannot have additional ICs attach (ICs cannot attach to a MC or unit containing MCs unless given special rules to do so, as is the case of the Dominus in this formation), thus preventing use of Psychic Powers like Gates of Infinity or Levitation to improve its mobility, there is a very real possibility that a savvy opponent will simply “kite” this unit all game long, shooting it to death or ignoring it while never allowing the Cohort to get into close combat.
This is where Lias Issadon comes in. With his WL Trait allowing him the ability to Infiltrate himself and 3 other non-vehicle units, he can Infiltrate the Cohort Cybernetica to within 18″ of the enemy DZ (or 12″, if you have blocked LOS) before the game even begins. Better yet, he can infiltrate the unit into cover and turn 1 you can activate the “Shroudpsalm” Canticle, giving them either Stealth, Shrouded, or Stealth+Shrouded, depending on how many Cult Mechanius units are in you army.
Combined with terrain, that means the unit has between a 4+ and 2+ cover save in addition to its 19 wounds at majority T7, 3+/2+ armor, and the Dominus’ ability to repair a single wound each turn on a roll of 2+. Use the Aegis Protocol in conjunction with all this to give the Kastelan Robots FNP and give the Dominus the “Autocaduceus of Arkhan Land” relic to give the entire unit IWND and, even if your opponent dedicates his entire army’s firepower toward the Cohort, you will likely be able ot weather the storm with plenty of combat power left in the unit.
Once you get to turn 2-3 move up, shoot as required, and charge your opponent’s DZ with the force of a unit of T7 Monstrous Creatures. Basically, infilitrating a Cohort Cybernetica is what Carnifex Broods would kill to do, but the Cohort does it AND still has effective shooting between the Kastelan’s Heavy Phosphor Blasters (switch to Protector Protocols if you need to shoot and then you are putting out 24 x S6 AP3 shots a turn), the Datasmith’s Gamma Pistols, and the Dominus’ Eradication Ray and Macrostubber. Intelligent use of the Canticles of the Omnissiah and split firing the Kastelans as required only makes this battle group even more effective and truly adds a balanced, capable, and potent “anvil” unit to your army.