Bow and Arrow of Nemesis

The Bow and Arrow of Nemesis were two objects required by the statue of Nemesis to achieve critical mass and thereby achieve a functioning state. These items consisted of a bow and arrow, both of which were made from the Time Lord substance known as validium, just like Nemesis. (TV: Silver Nemesis)

The Seventh Doctor was able to manipulate Lady Peinforte, who possessed the arrow and De Flores, who possessed the bow, to convene on the place where Nemesis (in comet form) was to land on November the 23rd, 1988. He then used them to reactivate Nemesis and used the newly awakened weapon to destroy the Cybermen's cyber-fleet. (TV: Silver Nemesis)