The 1-Second War

The 1-Second War is a war that took place in Bowser's castle, where Mario demanded he would not be evil anymore.

The story
The war actually lasted 10 minutes in slow motion, but it's considered one second long because Luigi decided to slow down time 600 times. Mario grabbed a Mega Mushroom and stomped on Bowser, but that took nine minutes (0.9 second) to do. Bowser was squashed and said he'd never be evil again. Mario took his word for it, and gave him a 1-Up Mushroom.

Aftermath
Ever since the war, (which was over for about seventy-three seconds by now), Mario and Bowser have been talking about how there are an infinite number of parallel universes over tea. Mario tapped the table, and they were in the parallel universe where the war actually lasted one second and Luigi wasn't an idiot.