Tunnel Crawlers

Use this Stratagem in your Charge phase.
Select one Area Terrain feature. Until the end of
the turn, each time an infantry unit from your
army declares a charge against an enemy unit
within that Area Terrain feature:
•Enemy units within that Area Terrain feature
cannot fire Overwatch or Set to Defend.
•That genestealer cults infantry unit ignores
the effects of the Difficult Ground trait.