Is there any consistent way of doing the Bowser fight? I understand the fireball skip at the beginning but am in need of learning how to fly above until I can get the next hit with the clown car.

Also, I'm making a return to the community. Nothing epic or grand though.

Lachurs made a NSMBUDX tutorial:

https://www.speedrun.com/nsmbudx/guide/im1je

If you only want the bowser fight:

This helped, thanks a lot.