Army of Meanwhiles and Neverweres

The Army of Meanwhiles and Neverweres fought in the Last Great Time War under the command of the Could've Been King. (TV: The End of Time)

The War Doctor fought against the troops of Neverwere, (PROSE: A Prologue) and the Tenth Doctor later mentioned this Army as one of the horrors that could be released when broke the time-lock on the war, along with the Nightmare Child, the Skaro Degradations and the Horde of Travesties. (TV: The End of Time)

Other Information
The Sixth Doctor thought of the time demon as a "neverwere," an "idea that got above its station." (AUDIO: The Wrong Doctors)

After the total event collapse, the Eleventh Doctor referred to the stone-like echoes of the Daleks and Cybermen scattered around the Pandorica as the "footprints of the Neverwere." (TV: The Big Bang)

Amy Pond battled Never-weres from an alternate reality who had invaded her mind. (COMIC: Ghosts of the Never-were)

Behind the Scenes
The Dangerous Book of Monsters dedicated a page to Neverweres, describing them as creatures that should never have existed, build from pieces of evolution that never happened.