Doctor Who has almost no boundaries. A show with an unprecedented premise has almost no set rules, excepts for the ones that it sets for itself. And even those don't seem all that important sometimes. This is as true with the villains as it is with the plots and heroes. Some villains are so well-received that it may be too tempting to show runners not to bring them back, no matter how much closure that there was at the end of the episodes. Other villains are so effective in single doses that further appearances lessen just how frightening they are as being the bad guys (and yes, I am talking about a specific species. But I'll get to that.) There are some ideas constructed in the reboot that we can say are hypothetically interesting--finding out the Doctor's name, seeing the destruction of Gallifrey, watching Eight regenerate into Nine--but that we really don't want or need to see happen on our TVs. It's actually the root of fan fiction and fan videos and daydreams that we totally don't have when we're supposed to be paying attention to something else. Logically, it's almost certain that some of these villains won't return. Impossible, even. Nevertheless, this is a sci-fi television show that has lasted for half of a century about a time-traveling alien who can change his whole body and personality. A little bit of rule-bending is to be expected. After all, as Matt Smith is either the Eleventh of Twelfth Doctor (depending on John Hurt's role in the upcoming 50th Anniversary special), current show runner Steven Moffat is soon going to have to find a way to wriggle past the 12-regeneration rule to keep Doctor Who going. Besides, Moffat seems determined to make nothing on the show absolute; pulling some unlikely villains from past episodes wouldn't be much in comparison. There are a lot of villains in Doctor Who, some of them much better than others. The problem is that contextual legitimacy matters a lot more than some writers and producers seem to sometimes think. Here are some of the rebooted villains that should be left behind.