In the StarCraft II: Wings of Liberty campaign, mercenaries are more powerful versions of basic units. Mercenary contracts may be purchased with credits from Graven Hill, a recruiter in Hyperion's cantina.[1] A mercenary unit may only be hired after its base unit is unlocked by playing the appropriate campaign mission. The War Pigs are the exception; they are hired free of charge after "Zero Hour".
During missions, a mercenary squad is trained at a merc compound. They have no build time, and arrive nearly instantly at the compound by drop pod. There is a short cooldown until the mercenary squad may be trained again. The squad size varies by the unit, and there is a limit to the number of squads that may be trained for each mercenary per mission. Mercenaries benefit from armory upgrades and lab research that benefit their base unit.[2]
Mercenaries have unique unit models—60% of the model is altered to ensure the models are unique, but still recognisable.[3]
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