Board Thread:The Panopticon/@comment-1293767-20151029072618/@comment-5918438-20160109053143

Yeah, I don't think so either. That was not a reflection of my actual views; rather, just a little foray into what could make the finale count. I agree she wasn't really a guest character at all, though. I was thinking setting clause, but if we want to discount the brief appearance of Churchill at the end of The Beast Below, it'd be hard to make an argument for counting Gallifrey, which is a setting only at the very end of Heaven Sent.

In light of that, I made some modifications to my original proposition (which you'll notice as you read through the more recent messages), which allow for community discussion and sufficient evidence in the form of exec statements to qualify a story without a guest character at all (in at least one of the episodes) to meet rule #3 nevertheless.

Heaven Sent is the only example of that thus far which I can think of. In such an odd case where one of the rules is not even applicable (where the designation "guest cast" at all is N/A, or "director" is N/A, etc), and only in such a case, discussion—hinging, of course, on good, solid evidence and all other requirements being met—may qualify that story to be a two-parter just like any other.

This does not change anything else, though. In any story where all episodes have at least one guest character, there must be at least one guest character in common between the episodes. With only one very specific exception, it's not a two-parter unless both parts share at least one guest character.