In contrast to the previous point, not only should Doctor Who not rely too heavily on old monsters, they also shouldn't make an effort to come up with too many new ones. There needs to be an even mix of classic Doctor villains and new creatures spread out through the season to keep things fresh while still paying respect to its own past. Some of the greatest monsters in the history of the series have come from the new generation, but there are just as many we wish never existed. Killer Santas come to mind.