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.
It was later discovered by two humans who had eluded Dalek capture that the Horrorkons were surprisingly docile, having a savage appetite only for metal. (COMIC: Monsters of Gurnian)
The Seventh Doctor battled against either a Horrokon or a Terrorkon in London's swers (GAME: Dalek Attack)