Walkthrough: Mario and Cappy will enter the Metro Kingdom in New Donk City on a rainy night. Immediately after they do, they will be alerted of some terrible creature crawling over City Hall, as Bowser continues to hold Peach above the building. On a nearby rooftop is Pauline, the mayor of New Donk City, who is in a bit of a sticky situation with Bowser showing up in her town. Begin your journey to stopping him by head to the right from where Pauline stands, directly across the narrow beams that hold more Purple Coins. Continue to make your way across the beams to the Spark Pylon, and then head down into the city outskirts.
As you enter this area, worm-like creatures will transition into Stingbys that will attack Mario. However, Cappy can destroy the creatures when they are still but worms, making these not too much of a bother. Directly to the left of this area will be a Sherm ready to attack you, located right by the next Crazy Cap Store. The path to the left will lead to a dead end, but it will also hold a scooter Mario can use to quickly get around the city.
Since there is also a roadblock to the right of the store, you will have no choice but to head down the street that has two Sherm Tanks. Dodge them to get by, or capture one with the help of Cappy to destroy the other as well as the Stingbys. However, at the end of this road will be yet another roadblock. This will force Mario and Cappy to take the detour route into the Construction Site. But before heading off there, use the Sherm Tank to break the blocks under a girder to find some Coins.