Gargoyle's are more stronger, lethal versions of the standard zerg guardian. They are special species of Surtur Brood, and they was used in Brood War by UED to capture Terran Dominion Psi-emitters. They appear in Covert Operations
Before death of the Overmind. Surtur Brood commanding by the Cerebrate Kagg, use Gargoyle's to fast destroying opposition on Antiga Prime, Mar Sara, and Chau Sara, and then infest those planet's. Many of them died from the orbital Protoss attack on this planet's.
When the Second Overmind was slaved by the UED. United Earth Directoriate send a Slaved Surtur Brood for test, to capture Terran Dominion Psi-emitters hidden on the planet Hydrax. A Group of these creatures was there to help Zerg in the ground battle.