Sam Marin originally auditioned for Skips, and Mark Hamill originally auditioned for Pops. Marin and Hamill switched roles after their voices didn't sound right for the characters for which they auditioned.
Regular Show made heavy use of licensed music, which is uncharacteristic for Cartoon Network shows. The selection consists mostly of 1980s music, like many of the references in the series, and most likely reflects the music J.G. Quintel grew up listening to.
High Five Ghost is the only character to have a shadow.
One of the initial concepts for Regular Show featured two animal characters, similar to Mordecai and Rigby, working at a zoo where the roles of humans and animals were reversed. The series was to be called Normal Show.
Adventure Time (2010) and this show were the first Cartoon Network shows to be renewed past six seasons.