Sometimes the best description is no description at all.

After the whole incident with Bowser trying to marry Princess Peach,Mario and Cappy have been living in peace and harmony.But that peace and harmony doesn't last forever,of course.Later,Bowser captures Princess Peach again,but this time,he takes the whole Mushroom Kingdom with him and plans to have a celebration ceremony,in honor of Princess Peach becoming his queen and himself becoming the king of the Mushroom Kingdom.Mario and Cappy then meet a bunny human girl named Delight and now it's up for all three of them to travel around the world once more and stop Bowser.You know what they say,"All for one and one for all!"