Two years ago, I played the game mentioned in the title. The game had two balls (armed with guns)
that you played as, and Mario, Luigi, Peach, Yoshi, and Toad make their
appearances as characters you kill! Yes, the game also covers
other games and shows (can't be bothered mentioning it). Mario plays as the main
villian, who is called "Dario" and is fought twice, Luigi plays as a boss after you beat
Dario for the first time, but is not named. Peach is called "Princess B****, who is optional
to kill, and Toads and Yoshi's will try to kill you as normal.
I am lazy at the moment, so I will edit this info later