I always figured that if they ever did a proper Mario/Sonic crossover, it should be an RPG. Not by Bioware, but by Alphadream, so I'd basically expect it to play like a Mario & Luigi game with Sonic in it. You want a plot? Robotnik doing a thing with the Chaos Emeralds, while Bowser is doing a thing with the Power Stars. Mario/Sonic show up to fight Robotnik/Bowser, the emeralds/stars go unstable at the same time, worlds merge together, boom. Sega and Nintendo should totally write me a check.
I've actually put a lot more thought into this than I should, but I don't want to sound like one of those people who go on and on about their game idea that will probably never happen, so. :P
edited 25th Apr '13 12:00:07 PM by Bobinator