It's muffin time / mr. muffin

the joke originates from Asdfmovies, or more specifically, the muffin song. the first ever appearance of the song was in, "World of light - Super smash bros ultimate" released on Jan, 1, 2019. here is a list of his or her's appearances,
 * World of light - Super smash bros ultimate
 * Once upon a time - Undertale
 * Mother earth - Mother
 * Gourmet race (64) - Super smash bros ultimate
 * overworld theme (JP) -Super mario world
 * Snow halation - 5 subscriber special
 * A certain someone's memories - MOTHER 3
 * Also appears in the 3rd design of banner and profile picture