A Perfect Ambush

When this unit is set up on the battlefield as reinforcements as a result of being set up underground, you can use this ability. If you do
so, select one enemy unit within 12 of this unit.
Until the end of the turn, each time a model in
that unit makes a ranged attack against that
enemy unit that enemy unit is now treated as
having a crossfire marker and as being exposed
for that attack.