Ordinatus Aktaeus

Instead of using the normal rules for Subterranean Assault, when a model with this special rule enters play via Subterranean Assault, place an Apocalyptic Blast marker (10") anywhere on the battlefield that is at least 1" from any enemy model, battlefield edge or piece of Impassable Terrain and then scatter that marker (see the Scatter rules on page 152 of the Horus Heresy: Age of Darkness rulebook).
If the marker’s final position is within 1" of an enemy model, any battlefield edge or a piece of Impassable Terrain, then the controlling player’s opponent may move that model to any position within 18" that is more than 1" from any enemy model, battlefield edge or piece of Impassable Terrain. If there is no suitable position within 18", then the model may be repositioned by the controlling player’s opponent anywhere on the battlefield that is more than 1" from any enemy model, battlefield edge or piece of Impassable Terrain.
Once the final position of the marker has been determined, the controlling player may place the model with this special rule on the battlefield so long as the centre of the marker is underneath part of the model’s hull, and the model remains more than 1" away from any enemy model. After the model has been placed, each Fortification within 6" of it immediately suffers D6 Str 10, AP 2 Hits, and nearby units suffer one S10, AP 2 Hit for each model within 6" of the model. Any unit that suffers one or more Hits from this effect must take an immediate Pinning test.
The area under the Apocalyptic Blast marker (10") is treated as Difficult Terrain and Dangerous Terrain for the remainder of the battle.

At the end of each of your turns, roll a D6 for each of your models with this special rule that has less than its starting number of Wounds or Hull Points, but that has not been removed as a casualty or destroyed. On a roll equal to or greater than the number in brackets associated with the special rule, that model regains a Wound, or Hull Point, lost earlier in the game. For example, a model with It Will Not Die (5+) would regain a lost Wound on the roll of a 5 or more.

When a model with this special rule is destroyed, the damage caused by its Catastrophic Damage is altered depending on the value of (X) in the version of this special rule as follows:
Magna: When destroyed, a model with this special rule resolves Hits caused by Catastrophic Damage as Destroyer attacks.
Major: When destroyed, a model with this special rule resolves Hits caused by Catastrophic Damage as Destroyer attacks at AP2.
Maxima :When destroyed, a model with this special rule resolves Hits caused by Catastrophic Damage as Destroyer attacks at AP2, and doubles the range of the Catastrophic Damage effect.

A model with this special rule has an Invulnerable Save of 5+ against Shooting Attacks.

Before the start of the first turn, when placing units into Reserve, a player must assign all units with the Subterranean Assault special rule and any Infantry units Embarked upon them to perform a Subterranean Assault. All models in a unit assigned to a Subterranean Assault must have the Subterranean Assault special rule, or be Embarked on a model with the Transport Subtype that has the Subterranean Assault special rule itself.

When rolling for Reserves, roll a single dice for all of the units assigned to the Subterranean Assault rather than rolling separately for each unit. If the roll is successful and the controlling player chooses to bring them into play then all of the Subterranean Assault units must enter play in that turn and follow this procedure:

Performing a Subterranean Assault
Once a Reserves roll for the units assigned to the Subterranean Assault has succeeded and the units are to be brought into play, the controlling player selects a single unit to deploy first. That player must place a single model with the Subterranean Assault special rule that is either a Dedicated Transport or a unit of its own (this model may have a unit Embarked within) anywhere on the battlefield that is at least 1" from any enemy model, battlefield edge or piece of Impassable Terrain and then scatter that model (see the Scatter rules on page 152 of the Horus Heresy: Age of Darkness rulebook).

If the model’s final position is within 1" of an enemy model, any battlefield edge or a piece of Impassable Terrain, the controlling player’s opponent may move that model to any position within 18" that is more than 1" from any enemy model, battlefield edge or piece of Impassable Terrain.

If there is no suitable position within 18" then the model may be repositioned anywhere on the battlefield that is more than 1" from any enemy model, battlefield edge or piece of Impassable Terrain.

Once this first unit has been deployed, roll a dice. On the roll of a ‘1’ the Subterranean Assault is Disordered, and the opposing player may deploy each remaining unit in the Subterranean Assault anywhere within 12" of the first unit without scattering, though no model may be within 1" of an enemy model or within Impassable Terrain. If the roll is a ‘2’ or higher, the controlling player deploys each other unit anywhere within 12" of the first, though no model may be within 1" of an enemy model or within Impassable Terrain. Any models Embarked on a model with the Transport Sub-type must remain Embarked and may not Disembark as part of a Subterranean Assault (but may Disembark normally during the following Movement phase).

Once all units are deployed, any enemy units with one or more models within 6" of any unit deployed as part of the Subterranean Assault suffer D6+3 Str 6, AP 4 Hits (Wounds caused by these Hits do not cause Morale checks or Pinning tests). Once all Hits are resolved, any enemy units that are neither Pinned or Falling Back and are within line of sight may choose to make the Interceptor Reaction (see page 309 of the Horus Heresy: Age of Darkness rulebook) targeting any one of the units deployed as part of the Subterranean Assault. Note that no Reaction other than Interceptor may be made against the deployment of a unit as part of a Subterranean Assault.

Once all units from the Subterranean Assault have been deployed and any Interceptor Reactions have been resolved, the turn proceeds as normal. Units that have been deployed as part of a Subterranean Assault may Move, Run or Shoot as normal. However, only units deployed aboard a model with the Transport Sub-type with the Assault Vehicle special rule may declare and resolve a Charge and Assault as normal. Other units deployed as part of a Subterranean Assault may not declare or resolve a Charge on the same turn as they are deployed.