Questions About The Multiverse

How big is the multiverse that is accessible from Poul Anderson's intercosmic inn, the Old Phoenix? Is every kind of fiction and myth real somewhere? The multiverse is certainly vaster than Anderson's own canon. There are different sets of dramatic and fictional characters and even different pantheons. Are there worlds of anthropomorphic animals and cartoon characters with appropriate laws of physics?

When a daily newspaper featured three comic strips each with only three panels per day, I thought that they were a single continuous story and did not understand why the realistically-drawn characters never met the cartoonish characters. Little did I suspect that what I was asking for was a multiversal crossover.

Again, it is cleverer when diverse genres can somehow be fitted into a single fictional universe. When Superman, usually drawn realistically, visited Plastic Man, usually drawn cartoonishly, Supes was also drawn cartoonishly because, it was explained, the drug that gave Plas his stretching power also affected his perceptions. Anderson would have been able to cameo such character interactions just as he did cameo that near-as-dammit-a-superhero, the Lensman, in the Old Phoenix.