To use the code, launch Doctor Who: Legacy, open the options menu and select the promo code tab. The code expires at the end of the year.
Playing through part two of the War Doctor levels will unlock a secondary costume for Cinder. Doctor Who: Legacy is a free iOS and Android game featuring Doctors and companions from the annals of Doctor Who history, including the most recent regenerations. It debuted in November 2013, soon after the Day of the Doctor BBC special.
Friendly reminder: the Doctor Who Christmas special airs on December 25 at 6:15PM GMT (1:15PM EST).