Driller (Level 1): Take a brown Crystal with a cost of 1 from the Mine. This action does not count as mining, therefore it does not interact with other skills or Artifacts that affect the Mine action.
Foreman (Level 2): The skill of this Mercenary allows you to Recruit Mercenaries for less. You can Recruit levels 1, 2, and 3 Mercenaries without using a card, and you can Recruit a level 4 Mercenary using a level 1 card.
Sergeant (Level 3): The skill of this Mercenary allows you to take up to 2 Mercenaries from the bottom of your Base into your hand. The hand limit applies as normal, so if you have 6 cards in hand you can only take 1 Mercenary.
Colonel (Level 4): The skill of this Mercenary allows you to take any number of Mercenaries from the Docks, provided that the sum of their levels does not exceed 5.