The model follows the rules for Ambush, with the following exception. Instead of entering the Battlefield from the Board Edge:
1. Choose an arriving unit with Underground Ambush.
2. Place the unit anywhere on the Battlefield in a legal formation more than 1″ from other units, Impassable Terrain, and the Board Edge.
3. Roll a D6:
• If 5–6 is rolled, the unit arrives where it was initially placed.
• If 1–4 is rolled, move the unit (without changing the direction it is facing) 2D6″ in a randomly chosen direction. If this would bring the unit within 1″ of other units, Impassable Terrain, or the Board Edge, the unit stops 1″ short of them and each model in the Ambushing unit must take a Dangerous Terrain (1) Test. The unit may then perform a Pivot (and must follow the Unit Spacing rule after the Pivot). None of these manoeuvres prevent the unit from moving following the rules for Ambush afterwards.
4. Repeat steps 1–3 for all other arriving units with Underground Ambush.