I'd make it so at the end of Mario, peach slaps Mario and goes to make babies with bowser. So the next game is called Mario's revenge and he goes off to kill both of them. Some of Mario's friends have inspirational quotes about how revenge isn't the answer, but Mario doesn't listen. So he gets to them and when he kills them at first he's happy but then he realizes what he's done and it haunts him forever. The next game you pay as Luigi trying to get Mario to snap out of it [spoiler]he's also developed a mushroom addiction[/spoiler] and you try and get him all these psychiatrists but it doesn't work. Towards the end you play as Mario again and you're really depressed. You go to talk to Luigi but them sometime tells you "but Mario he's dead, he's been dead for seven years. You killed him."