Let's Kill Iggy!

Iggy Koopa has watched his father lose to Mario enough times to draw a conclusion: the strategy of running in, grabbing the princess, and hoping things work out does not work and will never work. Iggy, unlike his father, has access to a form of dark Koopa magic that none of his siblings know about. He used it to claim control of a hidden Dark Realm deep in Koopa territory, brainwash a portion of his father's army into serving him exclusively, and begin planning an invasion of the Mushroom Kingdom on a timeline of his own choosing. The Mushroom Kingdom found out anyway — defecting Koopas warned the royal family — and Mario has been called to go into the Dark Realm and deal with Iggy directly.