ADEPTUS MECHANICUS: SKITARII
Harnessing the destructive energies of forge worlds within their weaponry, the Vanguard are so soaked in radiation that even to approach them is to confer a death sentence upon yourself. Victory for them is pyrrhic, as this radiation burns through even their heavy armour plate, slowly poisoning them to death even as their carbines bring about the(much quicker) demise of their enemies..
More Info: Warhammer Official