Shadow

A shadow was a dark image made by an object blocking light.

All Faction Paradox agents lost their shadows. (PROSE: Unnatural History) When the Third Doctor regenerated on Dust, he became infected with the Faction's biodata virus, and when he began to succumb to it in his eighth incarnation, he lost his shadow. (PROSE: Interference - Book Two) This occurred during a visit to San Francisco in 2002. (PROSE: Unnatural History) The Faction gave him a false shadow so he wouldn't notice. (PROSE: Interference - Book Two) He later lost his shadow again, but regained it following the destruction of Gallifrey and the Faction, which restored his original timeline. (PROSE: The Ancestor Cell)

Salim tried to steal Ace's shadow, but was stopped by the Seventh Doctor. (AUDIO: The Shadow Trader)

Abaddon's shadow killed every human it touched; when it touched Jack Harkness, he died as well, but the excess life-force also killed the demon. (TV: End of Days)

Some creatures seemed to be made of shadows, such as a shadow creature encountered on Charon, (PROSE: Pluto) the Elemental Shades (TV: Love & Monsters) and the Vashta Nerada. (TV: Silence in the Library)