Horrorkons were two-headed monstrous creatures native to the swamps of Gurnian. Originally believed to be vicious and unruly, the creatures were kept in check by patrolling Marsh Daleks. (DWA: The Dalek Book)
It was later discovered by two humans who had eluded Dalek capture that the Horrorkons were surprisingly docile, having only a savage appetite for metal. (DWA: The Dalek Book)