There was a joke on the Nanowrimo boards one year about how there was no story that could not be improved by the addition of ninjas. Many writers took this to heart and included ninja scenes
On a smaller scale, one of my fellow program directors at my summer camp job has an imaginary friend named Bob the Dragon who she has trained the little ones to believe is real (there are some artful props which enhance this mythology). We've all been told to encourage this (although the director involved can be kind of a brat about it) and when a child asks me a question such as do I know about Bob the Dragon or have I seen him etc. I always answer yes. I have a small stuffed bird I use in my own programs as a teacher and I expect my colleagues to play along with me, so I am happy to help spread the lore of Bob the Dragon when called upon.