10 Doctor Who Villains Who Actually Won
5. The Dream Lord (Amy's Choice)
The Dream Lord, as played by the fantastic Toby Jones (who is also the voice of Dobby - try watching Harry Potter after making that link) traps the Doctor, Amy, and Rory in two separate realities: one where the Ponds live in domestic bliss, and the other where they are travelling in the TARDIS.
He tasks our heroes with finding out which reality is real, and which is fake. In the end, it turns out that both worlds were a lie, and the gang manages to escape the Dream Lord's clutches.
The Dream Lord was actually the result of a really bad trip after some psychic pollen got into the TARDIS. Sure, "psychic pollen". Is that what they're calling it these days? Despite not being real, the existence of the Dream Lord rocks the Doctor to his core, as he has just witnessed what his dark side can do.
It's hard to establish what the Dream Lord's exact goal was, but he definitely seemed like he was out to expose the Doctor's flaws, so in that case, mission accomplished.