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 and Amon's forces 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.
The development team considered adding scourge as an unit for zerg in Versus during the Legacy of the Void expansion. However, they found that due to how units lacked a deceleration time when set on patrol, scourge was countered too easily if enemy air units were simply put on patrol. As changing this would require fundamentally changing the behavior of the engine, the idea was dropped.[6]
↑Blizzard Entertainment. Heart of the Swarm beta Map Editor. (Activision Blizzard) (in English). September 4, 2012
↑08-15-22 [Artosis returns to host PYLON SHOW Ep.154 - ft. members of the Frost Giant team as we chat about Esports & Competitive Design https://www.twitch.tv/videos/1504802534], Twitch.tv, 08-15-22