Walkthrough: The fight with RoboBrood will begin with it firing cannonbals form its chest. After a certain amount of bombs, it will also spit out a random Pokio. Quickly capture the bird, using it to poke the bombs RoboBrood is shooting, sending them back at its feet. Do this two times, and the metal outer shell on the robot's legs will explode, knocking the it back and exposing one of the Broodals on top. Flick yourself (still as the Pokio) up the legs onto of the robot, poking the exposed Broodal to deal damage. Repeat this process again after you do, this time avoiding the giant steps of RoboBrood. Blow up the legs again to knock the robot down once more, taking out a different Broodal this time around.
After doing this, RoboBrood's legs will begin glowing as it begins to charge at you. It will take several moments of running in place before it begins moving forward, so you this time to plan your dodge in order for it to run right by you. After it begins slowing down, the robot will begin launching spinning firecrackers at you. These two can easily be pecked away, and after doing so, it will resume shooting bombs like before. Deflect these bombs again, exposing the Broodal at the top of RoboBrood. Attack this Broodal to proceed to the final phase of the battle.
In the third and final phase of this battle, RoboBrood will advance quite rapidly, forcing you to constantly move to avoid it. Dodge the spinning firecrackers like before, waiting for your chance to attack when it reverts back to shooting more bombs. Do just as before to expose the final Broodal, attacking it to defeat the mechanical beast once and for all. After doing so, you will obtain a Multi Moon and will be allowed to proceed to Moon Kingdom in order to find Bowser. If you don't have enough Power Moons just yet to head there, quickly explore the massive kingdom in order to have enough to make your departure. Once you have the necessary amount to leave, fire up the Odyssey Airship and head to Moon Kingdom for the final showdown.