Based on a Dream: Multiple of the Mushroom Kingdom TV shows were inspired by dreams the creator had. One such show, Lady Greendress' Dream Journal, consists of many such dreams that were not adapted into in-universe entertainment, and even some that were, with the relevant episodes of that show ("The Origins of Rescube Squad Alpha", "Within the School", and "The Gorilla's Power is Fruit" respectively) referencing this fact.
Word of God: According to the creator, the characters of Illumina, Rosa, Evan, Bastu-Baby and Sweetie Cutie (from this video) were inspired by his experiences playing Tomodachi Life.
) were inspired by his experiences playing Tomodachi Life.