I had an idea somewhat like the luigio thing. LInk, zelda, and ganon, have to combine to form a new being. each of them has limited control over the body. if they fight too much, the trinity is broken, and they split up.
Anyway, subcon is where wart was from, but he was sent to the zelda dream world, where he takes on the identity mamu.
How's this for a plot, mario and luigi arre fighting bowser. kamek steps in and makes bowser super powerful. bowser uses a really strong attack that sends mario and luigi flying to separate ends of the koopa kingdom, where they are completely lost. you then alternately play as mario, and luigi, and try to meet back at bowser's castle. on the way, they meet a lot of characters unique to this game. when you meet, you can mix and match your party and go take on bowser.
The world would be a much cleaner place if people would eat their own trash.