Matchup help as Bowser Jr?

[Regulus]

I have difficulty countering really good bowsers who know how to play defensively as Bowser Jr. Any sideb approach can be punished from shield no matter how I land and he can outspace all of my moves. Tips?

 

[UltimaLuminaire]

Try mixing up jump canceling your side b approach. You can choose to fade away with DAir and threaten space. Even if Bowser chases after you, nothing comes out fast enough, or with enough disjoint, out of a run to contest a fade-away DAir. You could also fade in with DAir if you're confident the Bowser will keep shielding. Basically, if the Bowser is shielding a lot, that Bowser is setting themselves up to lose in this MU.