Stone Dalek

The Stone Daleks were a pair of Daleks left as an afterimage when Dalek history was temporarily erased by the universe's destruction on 26 June 2010.

A day to come
Through the extrapolations of the Matrix, the Time War-era Time Lords foresaw the Total Collapse Event Incident from the Doctor's personal future, which was recorded in the Dalek Combat Training Manual. Observing the effect total event collapse had on the Daleks, reducing them to stone afterimages, Time Lord Weapons Architects explored the possibilities of exploiting Localised Event-Collapse Time Fields as a means of petrifying whole fleets of Daleks. (PROSE: Dalek Combat Training Manual)

Total Event Collapse
During the Total Collapse Event Incident, (PROSE: Dalek Combat Training Manual) a Supreme Dalek, flanked by a Drone and Eternal Dalek, represented the New Dalek Paradigm at the Pandorica Alliance's sealing of the Eleventh Doctor in the Pandorica in 102. (TV: The Pandorica Opens) As the cracks in time continued to run rampant across the universe, Dalek history was erased, leaving two stone Daleks as petrified afterimages.

The Pandorica held atoms from the original universe, taken before the cracks erased events, which could sustain life. Light from the Pandorica restored one of the Daleks in 1996, albeit with limited power. This stone Dalek shot the Doctor, severely wounding the Time Lord without killing him but depleted its energy reserves nonetheless. It was confronted by River Song, who threatened to kill it by shooting its eyestalk with an Alpha Meson gun. Initially, it did not believe that River would destroy it, thinking that as one of the Doctor's companions, she would show mercy. River told it to look her up in its data banks. After doing so, it began to plead for mercy, shaking in terror. Later, when Amy and Rory asked where it was, she stated, "It died."

When the Doctor rebooted the universe and timeline, the stone Daleks, along with all things that had been erased from history, were restored to their original form and place in space and time. (TV: The Big Bang)

Props
The Stone Daleks were created using two of the five New Dalek Paradigm props originally created for Victory of the Daleks; what was the Strategist Dalek, as confirmed by director Toby Haynes (DWM 424), and the Scientist Dalek were modified to portray the active and inactive Stone Daleks respectively. Ironically, the remaining three props portrayed the Daleks in the Underhenge prior to total event collapse.

Other matters

 * Despite three Daleks appearing in the Underhenge, only two Stone Daleks are seen after total event collapse. From an in-universe standpoint, the original forms of the Stone Daleks remain unknown; unlike the original deep-voiced Supreme, Nicholas Briggs' portrayed the Supreme Dalek with a standard voice akin to the Drone Daleks in City of the Daleks and indeed the active Stone Dalek.
 * The reactivated Dalek was the first heard crying "Mercy!". The lone Dalek in Dalek cried for the Ninth Doctor to "have pity." The Twelfth Doctor recognized the word "mercy" as something improbable to hear from a Dalek, leading him to recognize Clara trapped in a Dalek housing, which inspired him to save the child Davros, thus implanting the concept of mercy into the Dalek's makeup. (TV: The Witch's Familiar)
 * An action figure based on the Stone Dalek was released by Character Options, named "Underhenge Dalek".