Walkthrough: By going to the left arena before Bowser's Castle, you will face the Purple Broodal you faced back in Sand Kingdom. This time around, she will have twin ponytails, each with a spiked bomb attached to the end. The battle will begin just as before, with her dancing around the arena while launching her ponytails at you. This time, however, lava will be left behind after the spiked bombs explode. You can try dodging all of these attacks, or you can prevent such things by constantly hitting her Cappy or by hitting the bombs right before they explode with your trusty sidekick.
After some time, she'll begin using larger bombs that will spin around the arena before slamming into the earth below. Avoid them until the land into the ground, and then throw Cappy at one in order for it to spin back at her and smack her right in the face. After it does, take advantage by jumping on her exposed head. After you do, she'll retreat to her hat and drop bombs down below at you. Like before, use Cappy to hit the bombs into the air before they explode. To end her assault even quicker, nail her with one of the bombs.
She'll repeat this same process two more times. Do the same thing throughout the battle, landing a second and then third blow to her head to finish her off once and for all. After defeating her, head to the arena on the right of the Golden Bowser Statues to face the final Broodal.