Nightmare Child

The Nightmare Child was something born during the Last Great Time War. Davros' command ship flew into the "jaws" of this creature during the first year of the war.

The Tenth Doctor stated, "I saw Arcadia destroyed. I laughed in the face of the Nightmare Child." after reliving a memory from his eighth incarnation. (IDW: The Forgotten)

Rassilon's plan to return Gallifrey to the universe in December 2009 would have led to the Nightmare Child, in addition to similar-such horrors like the Skaro Degradations, the Army of Meanwhiles and Neverweres led by the Could've Been King, and the Horde of Travesties, being pulled out of the Time War and into reality. However, the Doctor managed to prevent this from happening by severing the link that the Time Lords had to the rest of the universe, preventing them from escaping the oblivion of the Last Great Time War. (DW: The End of Time)

Behind the scenes

 * In Doctor Who: The Writer's Tale, it was referred to as 'the Dalek Emperor's Nightmare Child' in an early script draft.