They are ancient Serpentine and served Mambo the Fifth until Aspheera stole the throne using Spinjitzu (which Wu taught her as part of a deal). The Pyro Destoyers help Aspheera during the fire chapter (Ep. 1-15 of Season 11) along with Char, the Pyro Slayers, and the Pyro Whippers.
The Pyro Destroyer has the same torso and legs as Pyro Slayer and Pyro Whipper, and shares its head with the Pyro Slayer. Both this head and the shoulder armor also appear on Aspheera, but cast in gold rather than brown. The head would last be recast in silver for 76389 Hogwarts Chamber of Secrets.