Universal Rule.
The model gains Heavy Armour and Great Weapon.
At the start of any friendly Shooting Phase, a single model with Stygian Overseer may detonate a single Tunnel Marker within 24′′ of it. If so, all units within 6′′ of the Tunnel Marker suffer 2D6 hits with Strength 4 and Armour Penetration 1. Then remove the Tunnel Marker.