The taxon is represented by a single, nearly complete skeleton that was collected from the Sunspot Mine at Mazon Creek, Illinois.

Mann and Maddin (2019) diagnose Diabloroter by the following features: (1) long maxilla; (2) skull roof ornamented with radiating grooves; (3) circular pits on the prefrontal; and (4) a narrow and blunt snout.

They differentiate it from the European Batropetes by: (1) reduced lengthening of the mid-dorsal ribs; and (2) a less robust pectoral girdle.

They also differentiate it from the North American Quasicaecilia by: (1) less rounded skull; (2) reduced contribution of the nasals to the snout; and (3) more extensive lateral cheek.

Below is the strict consensus topology recovered by the maximum parsimony analysis of Mann & Maddin (2019): Seymouria Limnoscelis Petrolacosaurus Captorhinus Opisthodontosaurus Ophiacodon Dimetrodon Pantylus Llistrofus Micraroter Nannaroter Pelodosotis Huskerpeton Cardiocephalus Rhynchonkos Aletrimyti Dvellecanus Brachydectes Quasicaecilia Diabloroter Batropetes Carrolla