Good crossovers should always account for the respective series’ internal laws of physics.

Case in point, Naruto and Harry Potter crossovers; I always appreciate it when an author does remember that while Wizards have magic, they still need to point a stick at their target. Ninjas have a habit of being really, really fast and dodging shurikens that are probably faster than bullets (series internal physics). Furthermore, break their wands, get into their personal space, and wizards are pretty much hopeless. Having said that, Wizards probably has the upper hand when it comes to traveling, and other indirect magic; just think about the Weasleys’ house, or the Quiditch World Championship. In a war situation, the Ninjas would win as long as they do their homework properly, move in fast and don’t give the wizards a chance to fight back. The way I figure, the Wizards’ society is really badly prepared for war, however, give them time and they probably can utilize their spells in ways that will win over the Ninjas… that’s if the ninja doesn’t use their summons. Hmm, actually that raises the whole point of whether magic would affect Summoned Creatures.

Another example; Jedi are powerful, in the Star Wars Universe, but (after much discussion and thoughts, and I still think I’m right), Jedi would so get their arse handed to them in the Warhammer 40K Universe. Even if we allow characters from both Universes to keep all their respective powers and fight on neutral ground, Jedi would lose. Space Marine and Inquisitors tend to squash people that are, um, alien. In addition, the sheer level of power and genetic modifications, add the aerial bombardment capabilities… well, d00d, Coruscant would be a waste land in under 10 seconds. Though, the SW Universe does have the upper hand when it comes to hyperspace travel, no demons. The Warhammer 40K people would have to deal with the Warp… And I’m pretty sure the SW universe has faster space ships (thought I’m not 100% sure), either way, depending on the time frame, the distance they need to travel and so forth, characters from the Warhammer 40k will more than likely win… unless, all your Jedi are like Mace Windu in the Clone Wars cartoon…. Maybe.

The point; I LOVE crossovers that actually think through all the internal physics of each Universe. And one day I shall expand this, um, random piece of essay and have it make sense. (Coherency, I find is greatly lacking at the present time.)

Sleep now.