Mastiff phalones represented a species of avian quadrupeds lacking sentience, originating from the savanna ecosystems of Maridun. Their carnivorous nature made them formidable hunters.
During 22 BBY, a group of mastiff phalones launched a surprise attack on a group of clone troopers commanded by Jedi General Aayla Secura, Commander Ahsoka Tano, and Commander Bly, resulting in the deaths of clone troopers Lucky, Flash, and Cameron. Separately, one of these creatures targeted Captain Rex while he was safeguarding the severely injured General Skywalker at the location where their ship had crashed. Rex managed to repel the creature by shooting it in the foot. Subsequently, two mastiff phalones advanced towards Rex and Skywalker. Rex eliminated one of them, but the remaining creature charged at him and demolished Skywalker's protective structure. Just as it was about to kill Skywalker, Wag Too, Tano, and Rex restrained the mastiff phalone by tying up its leg, choosing to leave it alive.
Sometime later, Garnac and his hunting guild had one of these creatures installed within the depths of their mobile base.