Take Super Mario, and add the following characters with their specific game styles respective to their games:

- Link (Legend of Zelda)
- Samus (Metroid)
- Ryu Hayabusa (Ninja Gaiden)
- Megaman (Megaman)
- Bass (Megaman)
- Simon Belmont (Castlevania)
- Sophia III (Blaster Master)
- Bill Rizer (Contra)
- Luigi (Mario)
etc

And you have Super Mario Crossover, a fun crossover game that uses Mario Bros as the basis and while you are still able to play as Mario in his standard journey and gameplay, crossover allows you to do the journey as the other characters listed, in their specific gameplay styles, it's a great game I recommend you all to play,