Flame Falcons

A chapter of the 21st Founding who were, unsurprisingly, some of the unluckiest bastards alive. They suffered a geneseed mutation that caused them to burst into flames. Everybody thought this was a pretty awesome party trick until the Inquisition caught wind of it and decided "no Flame Falcons you are the demons". Fast forward, excommunicate traitoris, Grey Knight, everybody dies in a (larger than usual) fire.