When a battle is lost against the Night King or a White Walker, 1 unit must be lost from the domain before retreating (if you played a card, you ignore this). If at least 1 non-player Power Token was in the domain, that unit must be lost and it is placed in the Terror Pool. If it is a non-player Hero, it returns to its House Mat (gain its benefit like normal) and the Night King takes 1 Power Token from the house’s mat and places it in the Terror Pool. If only your units are in the domain, you must return 1 unit to your House Mat before the remaining units retreat. The Night King and White Walkers never gain victory points for winning battles.