Bub-ulber's role in the game isn't that significant but he does have a trouble that he needs done. Bub-ulber requests some hot dogs and a Mousse Cake. The hot dogs can be bought at Glitzville for 10 coins (make sure to buy two hot dogs since he will ask for another after he ate the first one) and the Mousse Cake can be made by giving Zess T. a Cake Mix that can be bought at the Pianta Parlor for 6 Pianta Tokens. After completing his request, Bub-ulber will give him a Dried Bouquet.
Mario can return to Bub-ulber anytime to receive more Dried Bouquets if Mario brings him more hot dogs.