Episode: The Waters of Mars So here they are, the best one-time villains, from David Tennant's best episode. The Waters of Mars is a chilling and utterly unforgettable special, complete with moral dilemmas, Lindsay Duncan, Time Lord victorious, and one of the most terrifying foes ever. Unlike The Vashata Nerada, The Flood are inspired but something rather tame, but once the waterborne infection spreads to the crew of Bowie Base One, the fear is ratcheted up a few notches. The Flood take the top spot not only for their fear factor, but for an intriguing and unique design. Their blackened mouths, cracked skin, hollow empty eyes and the copious amount of water leaking from them are the stuff of nightmares. It almost makes you scared to wash your hands. The Flood virus is a monster unlike any other on Doctor Who most villains who've appeared on the show are humanoid in appearance (with some notable exception) and most often villains who fail to conform to our expectation of alien life are quickly forgotten. Yet The Flood proved that a viral villain could be both memorable and terrifying. The Waters of Mars is not short of memorable scenes, yet the best involve The Flood. The scenes where the crew writhe and convulse as the virus infects their bodies are absolutely horrifying. Especially the scene where Steffi is infected, as she sacrifices one last look at the video of her daughters, before the water rains down on her. The Flood will long be remembered as one of the most original and terrifying villains since Doctor Who cranked back up again. Their first and last appearance gives them the top spot on this list, because in the end, the water always wins. If you think we've overlooked any great one time villains let us know in the comments below.
