Okay,this Is a crazy idea,and TC digital games,Konami,Bandai,Nintendo,and Tecmo would never do this,but I'm still gonna take a whack with the hammer.
I guess the fighting game would have SSB mechanics,except It woud be health meters.You'd also be able to use the Items from the different franchises,such as picking up equip items(YuGiOh),Battle Gear(Chaotic),and other assorted Items,with stages from the assorted franchises.
Now,I've been thinking up of the roster,so here's my choices:
1st Set: 2nd set: 3rd set: 4th Set
Maxxor Chaor Prince Mudeenu Odu Bathax
Dark Magician Blue Eyes White Dragon Elemental Hero Avian Cyber Dragon
Pikachu Charmander Bulbasaur Squirtle
Suezo Mocchi Tiger Golem
Agumon Veemon Guilmon Agumon 2
Here's the Items I could think of at the moment:
Axe of Despair
Liquilizer