Okay, he was cut from the former, had a badge effect in Paper Mario and had Booster as an expy in the third, but... if you could have a new Wario focused Mario RPG based on any of these series, which would you choose?
I have never played Super Mario RPG, so I don't know what his role could be or how he would fit in to the game, but between the two I have played I think Mario and Luigi would be the best.
I would love a game like Partners in Time where there's four playable characters; Mario, Luigi, Wario and Waluigi. The two sets could go around and fight separately but come together to do a double bro battle or something.
I think that a Mario and Luigi game would be a good fit for Wario, the humor is a good fit for him because if he was put into the game as a supporting character he would still be an excellent existing IP to put into M&L.
I really liked TTYD, and I kinda hope they will release another Paper Mario like that one one day. I think it could be really cool to have Wario in a game like that, too. I dont think he should actually be in the party, though. I think he should be a villain in the game : p I always thought Wario should have been used as an enemy of Mario far more often, and I think having him as the main rival (though not the actual main villain) in a game like TTYD could be alot of fun.
Maybe even do like what they did with Bowser in TTYD, and give him his own playable quest between storyline : 3
