I like crossovers.

There, I said it. It's a statement that doesn't really reflect well on my personal taste - after all, when most people hear "crossover", their brain translates it to either "cashgrab" or "unspeakably bad fanfiction" depending on the context. (Note: if the context is comics, "continuity nightmare" is also acceptable.) There's not really much I can do to argue against that - for proof of the former, direct yourself to any number of nonsensical promotional crossovers (recent example: Kingdoms of Amalur/Mass Effect), and for the latter you need only look at the great fanfiction site which shall not be named (whose crossover section, it must be said, makes for an excellent time with friends - the goal is to make everyone else scream in agony and horror before you do.)

But I like them anyways. Perhaps it's that I like the potential more than the common execution - when you crossover things, you're opening up a whole bevy of interactions and moments that would have been impossible had the series remained separate. If the settings are disparate enough, things can get really interesting - plenty of people joke about Doctor Who and Sherlock sharing an episode (in fact, the concept is common enough that it now goes by "Wholock"), but really, if you stop and think about it, what would that really do to the great detective? Sherlock Holmes is a man of reason, and an incredibly brilliant one at that. If the Doctor came sauntering into his life, I doubt it would take very long for him to detect something amiss about the man with the funny bow tie - and when the truth came out, what then? Oh, true, the Doctor's world still operates on some semblance of logic, but it's a logic that wholly overthrows that of contemporary Earth. We've seen Sherlock work himself to the bone to prove his view of the world is still accurate in "The Hounds of Baskerville", but faced with irrefutable evidence that his world is merely a shade of a galaxy of monsters and miracles, could he adapt?

That is the kind of idea that makes me grin, the kind of thing I like to prod with a stick and see how it reacts. Crossovers have so much inherent potential for challenge in them, and challenge drives characters to grow and change and, if you want to be Doylist about it, be entertaining to the readers. This isn't to say crossovers should be all dark, all the time, their only purpose to make a mockery of the characters - on the contrary, we expect characters to flourish in the new settings and make them their own. A few weeks back I wrote a little gag post where, through circumstances unexplained, the Toa Nuva had joined Commander Shepard aboard the Normandy. Sure, you could launch into a diatribe about the morality and acceptability of biomechanical life in a universe threatened by God-machines called the Reapers, but that's no good if you can't also have Joker throw out his one-liner assessments of the Commander's new allies. After all, half the fun of crossovers is, well, that basic appeal of "I like thing A, and I like thing B, so let's try thing A+B and see what happens."

Of course, that's a task easier said than done. Crossovers are by their nature a balancing act; include too much of thing A and not enough of thing B, and you get people wondering why even bother to make a crossover at all when you could sub in some original characters and just go ahead and make a new story about thing A. Some degree of self-control is also required; it's very easy to say, "well, we've got thing A+B here now, so let's give thing A+B+C+D a shot!" (Case in point: I above mentioned "Wholock". I now mention its brother "Superwholock" and its cousin "Superwholock-Potter", which I will leave for you to research on your own time.) Some authors try to dodge the problem by avoiding specific characters or explicit crossovers - I'm given to understand that the now-legendary My Little Pony/Fallout crossover fic Fallout Equestria in fact makes no attempt to crossover the two worlds, but rather combines them into a post-apocalyptic wasteland where ponies struggle to survive, the canon characters making no appearances. This can be a valid method, and indeed avoids some of the problems outlined above; the largest concern I have with this approach is that you run the risk of causing the reader to ask, "why not just make this an original story?" if you create too much from whole cloth.

(As an aside, I here would like to mention one other type of troublesome crossover: the setting of A with the characters of B, who possibly have assumed the personalities but not the names or appearances of the characters of A. Please avoid this.)

In short, then, the crossover is problematic yet fascinating. Done well, it can challenge each of the sources in ways otherwise impossible; done poorly, it causes the reader to ask what the point of the whole thing even is. Perhaps more than other fanwork, it lends itself to quick-and-dirty creations; if we take "A and B have now crossed over" as a given, that alone gives us enough quick material to entertain. But if we put in the effort, there is potential beyond the quick joke; there is the possibility that we can create something with just the right balance of old and new.

Anyways, the point is I'm actually partway done planning a fairly serious Mass Effect/Bionicle epic to be written after ME3 comes out and will be making a blog post about that sometime in the near future. But before that, I wanted to type out my thoughts on the genre as a whole and get some discussion from others.