Prologue to Battle! The Return of Mario! is the first episode of Super Mario Bros. Z Kai and the first episode of its version of the Bowser Saga. The episode first aired on April 5th, 2009. Its original American air date was May 24th, 2010.
The episode begins with a flashback of the destruction of Planet Bowser at the hands of Metal Sonic, and the upbringing of Mario on Mushroom World, as depicted in the original Super Mario Bros. Z series. Fifve years have pased since Mario's victory over Sonic at the Mushroom World Tournament, and he has since married Princess Peach, with whom had a brother named Luigi. Mario and Luigi (also known as the Mario Bros.) are heading towards a reunion with Mario's friends. Elsewhere, an odd-looking spacecraft crashes on Earth. A man with a battle armor emerges from the vessel and flies off to scout out a powerful lifeform. He locates it with the help of an Scouter apparatus located on his eye. Sonic is nearly killed by the stranger, but this is averted when the man leaves to scout out a more powerful lifeform. The other strong lifeform is Mario, who, at the Mushroom Kingdom, introduces his son to Yoshis, Toadsworth, Princess Daisy, and other citizens of the Mushroom Kingdom. The stranger arrives and speaks to Mario in a familiar manner.