The Cerberus Brothers are three vicious villains from the Extinctioners universe, although they can merge into a single entity (hence their name, a reference to the mythological guardian of the Greek underworld).
They made their first appearance in the webcomic, "Arctic Blue" and were enforcer of the arch-villain, Corruption - in this story they pursued Arctica with the intention of capturing her so their master could drain her powers.
The Brothers proved unable to beat Arctica as she used her cryokinetic abilities to literally freeze them, forcing Corruption to begrudgingly use on of his "tails" to free his henchmen, while his sister Pain looked in amusement and had the much more effective killers known as the Femme Fatales take over the hunt.
Although by no means a match for a hybrid of Arctica's level the Cerberus Brothers did manifest superhuman abilities, allowing them to merge into a single entity - gaining the strength of three adult canines all in one body and three independent heads - they can also separate back into three unique bodies at will.
They also show some degree of invulnerability as they survived being frozen in ice by Arctica, albeit they were unable to free themselves without Corruption's aid.