Iron Road

Walkthrough: You will enter Iron Road on a small bridge that will crumble if you stay on it for too long. Under it will be Purple Coins, as well as more even further below at the end of a platform that will also break away. On the road itself will be Piranha Plants that will be spewing poison everywhere. Cappy won't be able to control them, but he will be able to plug up their mouths just long enough for you to jump on and destroy them with Mario. After defeating them, head to back of the road where there will be many moving platforms and carefully cross them.

At the top of the platforms will be Uproots ready to attack you. Capture one with Cappy, and then look for the steps leading to what looks like a dead end. However, as an Uproot, you will actually be able to push on the ceiling to extend it, which will allow you a narrow area to enter from. After breaking through more bricks, head up to find a nut that holds a Power Moon. From there, drop down to the lower area, watching out for the Uproot that is waiting for you. Push up on the platform again to back up, breaking through the blocks to reach more Purple Coins from above. Drop down one more time to reach the next checkpoint.

Once you reach this checkpoint, leave the captured root and defeat the Piranha Plants with Mario and Cappy like before. However, before attacking them, head to the yellow pole by going to the ledge below the platform. On the right of it will be more Purple Coins, and on the left will be another Uproot that can be captured to open the nut ahead of it to obtain another Power Moon. After you do, head back to the Piranha Plant platform and use Cappy's Spin Attack to wipe away the poison. Have him get caught in the mouth of the Piranhas before defeating them like before with Mario.

At the very end of this platform, a giant Piranha Plant awaits Mario. Like the smaller Piranha Plants, you can use the same method with Cappy like before. Use Cappy to get lodged in the mouth of the giant Piranha Plant, causing it to fall to the ground. When it is down, ground-pound with Mario to cause serious damage. After the giant Piranha Plant is down, the next Power Moon will be Mario's for the taking.