Continuity bomb

A continuity bomb was a Dalek weapon developed during the Last Great Time War.

The bomb was programmed to target one individual, then alter one event in their timeline, changing their "continuity". The Tenth, Eleventh and Twelfth Doctors found one, but were unable to disarm it. This caused them to shift between three different timelines, one for each Doctor, where they made a decision which negatively affected them and the universe. (COMIC: Four Doctors)