The Dream Lord

The Dream Lord is the dark side of the Doctor, who has control over dreams. He was "awoken" by speck of psychic pollen from the candle meadows of Karass Don Slava that had gotten stuck in the TARDIS, and woke as it was warmed up. The Dream Lord drew his personality from the Doctor's inner darkness. He trapped the Doctor, Amy Pond and Rory Williams between two worlds, telling them that one was dream and one was real and that they would have to choose between them. However, the Doctor eventually realised that neither were real, and managed to return them all to the waking world. After removing the pollen, the Doctor saw the Dream Lord's face in his reflection in the TARDIS console, smiling slyly at him. (DW: Amy's Choice)