Upon collecting all 100 Shines in the game, you will be able to do battle with Fury Bowser one more time. As soon as you collect the last Shine, the game will force Bowser on you and he will not go away at all (especially since there’s no more Shines to grab). Head on over to any of the Giga Bells and collect one whenever Fury Bowser appears. No matter how much you damaged him with the Shines you collected while he’s out, Bowser will always have full health for this battle. Despite the different color for both Bowser and his health bar, the first bout with him is the same as when you faced him at 50 Shines.
During the second phase, when you’re chasing after him on Plessie, he’s definitely a lot more challenging. Not only is he faster in moving from spot to spot, which means you won’t get the same hits at the same points, but he will shoot out a lot more blocks as torpedoes. When he’s shooting out the horizontal lines of them, they become quite difficult to dodge, so hopefully you have some extra stock of power-ups available, in case. It might take you a few laps in order to get the four hits necessary to defeat Bowser here, but once you do, you will have fully completed Bowser’s Fury.
There’s not much of a reward for completing this expansion fully, although you will be able to explore the place without Fury Bowser’s threat looming over you. You will notice that Cat Mario looks a little different, as does Bowser Jr, which is the full extent of your reward for collecting all 100 Shines.