The Mecha Sonic Saga is the first (ongoing) saga of Super Mario Bros. Z. The story just begun by the saga. Mecha Sonic is the main antagonist of the saga who Mario must face. It's the story of Mario, along with Luigi and Yoshi, who joined the two hedgehog heroes; Sonic and Shadow to find the Chaos Emeralds and stop Mecha Sonic, who desires to destroy the Mushroom Kingdom, as well the whole Mushroom World.