The Spreading Corruption
(Rule)Description: All models in a unit made up entirely of models withthe Infantry, Cavalry or Dreadnought Unit Types inthesame Detachment as Horus Ascended may be giiven the Corrupted Unit Sub-type at a cost of +25 points per unit . If this upgrade is selected for a unit then all models in the unit must gain the Corrupted Sub-type – models that are attached to units, such as Apothecaries or Techmarines, must be upgraded separately. For Apothecary Detachments, Techmarine Covenants and other units which are bought as a single Force Organisation slot and then separated, divided or attached to other units (including units bought using the Retinue special rule or any variant of that rule which allows a unit to be counted as part of the same Force Organisation slot as a Leader model), the upgrade is bought once for the entire set of models before they are separated and must be applied to all models chosen as part of that Force Organisation slot.