In embracing mythopoeic promiscuity, [C. S.] Lewis was also following in the footsteps of his “master” MacDonald. In the fifth chapter of Phantastes we get the myth of Pygmalion, and in the sixth Anodos encounters Sir Percival; MacDonald is perfectly happy to have a wide range of mythological, legendary, and literary worlds knocking against one another. And if I were to make a defense of this procedure, I’d begin by noting that a great many myths and tales and legends are always knocking against one another in our own heads.Alan Jacobs
Once again, I’m put in mind of Edmund Spenser. If there are any rules governing which mythical, legendary, or literary characters may or may not appear in The Faerie Queene, I haven’t discovered them. But, of course, that’s one of the things that makes it so wonderful.