The story length in Super Mario Maker for 3DS isn't fixed. It depends on how much you get into the level creation and challenges. Generally, it can take a few hours to several days of dedicated play.
Well, in 'ds mario and luigi bowser's inside story', the game focuses on Mario and Luigi's journey within Bowser's body. There are different levels and challenges. You get to control both Mario and Luigi with their distinct abilities. The story also involves Bowser himself in a rather unique way, like seeing things from his perspective at times. It's full of humor and action.
If it's a crossover with Final Fantasy, Cloud Strife could be a main character. He could bring his sword - fighting skills to the Mario Party world. His serious and brooding personality would contrast with the more light - hearted Mario characters, creating some interesting interactions during the story and mini - games.
One idea could be a crossover with the Legend of Zelda series. Link could be a special guest in the Mario Party world, bringing his unique items like the Master Sword and Hylian Shield. He might participate in mini - games that require his combat skills or puzzle - solving abilities.
One of the main features is the unique gameplay mechanic where you get to play as Bowser from the inside. There are also lots of fun mini - games. The story is engaging, with Mario and Luigi teaming up in their usual wacky adventures within Bowser's body.