Horrorkon

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)

Trivia
The name of the Horrorkons appears to have been inspired by the Horrorcons from 1980s cartoon The Transformers. They were two Decepticon Triple Changer Headmasters, who transformed into animal forms (an ape and a dragon/tyrannosaurus rex) and into fighter jets, whilst their robot heads formed their animal heads and their jets' pilots.