The creator of Mob Psycho 100, known only as One, also created the acclaimed One Punch Man series.
The omake at the end of season 1,episode 12 was the authors debut as animation director. The rougher visuals pay homage to One's original art style.
The word One is seen in several scenes throughout the series, an obvious Easter-egg to the creator, known as One.
The number 88 is not included in the Season 1 theme
In multiple instances, there are easter eggs featuring Saitama from One Punch Man, ONE's (the creator) other series.