Fatality Index

The Fatality Index was used by a species from a planet that regulated how that species carried out executions.

was sentenced to death by this species and, in accordance with the Fatality Index, the Twelfth Doctor was chosen to carry out the sentence.

The Index can be used to look up how many beings have been killed by a single individual by searching for their name under cause of death. To intimidate the species, the Doctor had them look him up on the Fatality Index, specifically being the "Cause of Death". After seeing the incalculable number of victims attributed to the Doctor (largely due Cybermen and Dalek armies he's wiped out over millennia), they all fled in terror after the index sped up to a blur to list victims. (TV: Extremis)