Hell on Earth: Gimme Shelter
Doomsayers are the green-robed adherents to Silas Rasmussen's Cult of Doom. They serve as missionaries for his message of the chosen nature of Mutants and the coming doom of "normal" humans, and they use strange powers to channel radiation to hurry said doom along.
There is also a purple-robed order of heretical Doomsayers, loyal to the schismatic Joan, who look on their poor unmutated kinfolk with pity rather than scorn and protect them from the brutal ministrations of Silas's devout legions. The heretics wield the same powers as the devout cultists, but use them to help both mutants and humans and to fight against the Cult.