The Mushroom Kings are the Mushroom Kingdom's rulers that where transformed into different creatures by the Koopalings. They must be saved by Mario by retrieving the wand from the given Koopaling. They made their debut in Super Mario Bros. 3.
In New Super Mario Bros. D.I.Y., the Mushroom Kings make a return, as seven of the ten hostages that can be featured in the game. The appearances of the kings when they as not transformed is almost the same as in Super Mario Bros. 3.