Fungus Freeway

From the Super Mario Wiki, the Mario encyclopedia

The Fungus Freeway is a long highway in Brain Drain. Mario, Luigi, Princess Peach, Toad, and the Mushroom King investigate it while following the trail of people whose minds were swapped by Iggy Koopa's Synapse Switcher. They see that all of the traffic police had their minds swapped with Piranha Plants, causing traffic to become backed up for miles. By the end of the story, the group discovers that Fungus Up cures the mind swapping, and they insert it into the water supply, which eventually cures everyone in the Mushroom Kingdom.