3. Dark
The 11th Doctor was already moving in this direction post-Ponds. My 12th Doctor would leap onto this movement and bring it to new heights of subdued and sinister. He would wear mostly black; speak in a gravelly, low voice; and display far less emotion than previous Doctors. His empathy would be diminished, and he'd have moments of pure coldness that would send shivers down the spines of the viewers. Elements of darkness have always been present in the Doctor's character, but never before has it been a main characteristic (well, maybe the 7th...), but my 12th Doctor was going to be known, long after his tenure, as "the dark Doctor." He'd be distant perhaps even from his companion(s)and frighteningly non-emotive. Neither the viewer nor the Doctor's companions would ever quite know what the Doctor is thinking.