Festering Miasma

When: Your opponent’s Shooting phase, just after an enemy unit has selected its targets.

Target: One HERETIC ASTARTES unit from your army that was selected as the target of one or more of the attacking unit’s attacks.

Effect: Until the end of the phase, your unit has the Stealth ability. In addition, if your unit is a NURGLE unit, it can only be selected as the target of a ranged attack
if the attacking model is within 18".