Ranma/Bobobo-Bo-Bobobo: Do you REALLY need to know. Seriously, the very idea could blow your brain out of your head.
Whoa. Anything Goes meets Super Fist of the Nose Hair. Now, that's something to be afraid of...and that's drastically understating it. The first idea in that last list, though, I could definitely imagine.
My main idea is for Slayers/One Piece, although it would probably be somewhat of a stretch (pardon the pun). Events in both worlds would conspire to bring the Straw Hat Pirates (and several others) to the other universe, scattering them in the process. Before trying to get home, the crew would have to reunite in order to fight off a combination of threats from both worlds (I mean a literal combination, especially if they couldn't defeat the heroes on their own). I can imagine Ussop entertaining Amelia and Prince Phil with his tall-tales, Luffy clearing out the restaurant that Lina's sister works at, Zoro getting a reputation as a Bandit Hunter, etc. You get the idea.
If I think of anything else, I'll type it in later.






