SMSB is probably going to have an unlockables job right before launch, but for now I like to imagine the game starts you with just Mario; Luigi; Peach; Bowser; and Yoshi with Peach's Castle; Bowser's Castle; Melee Mushroom Kingdom; Mushroom Kingdom U; and either Star Road or Mario Circuit U, and characters and stages are unlocked in random order - every 2 battles for stages and every 4 for fighters. No challenger approaching battles.