Scourges appear in StarCraft II: Wings of Liberty as environmental ambiance in missions[1]; they appear in the protoss mini-campaign[2] and in the Char missions.[3] They are last seen as a special form of attack by leviathans, dealing 500 damage each.
The scourge is exclusive to Zagara in Co-op Missions, and require a scourge nest to mutate. Upgrades for the scourge are unlocked when Zagara reaches Level 4. As in the original StarCraft, scourges mutate in pairs.