Nasty Skulkers are not placed on the battlefield at the start of the game. Instead, make a note of which Goblin Mobs include Nasty Skulkers, and of how many they include. These units are referred to as 'concealing' units. At the start of its first round of combat, during Step 1.1 of the Choose Combat & Fight sub-phase, a concealing unit must reveal its Nasty Skulkers – they cannot be revealed at any other time. Position each revealed Nasty Skulker as you would a character that has joined the unit. Once placed, Nasty Skulkers cannot leave their concealing unit. If a concealing unit is destroyed or flees the battlefield before its Nasty Skulkers are revealed, they are removed as casualties.