Billy West declined to reprise his role as Stimpy or provide any voice work for this series. West alleged that the portrayal of Ren and Stimpy as homosexuals in "Onward and Upward" served as, in West's phrasing, 'an advertisement for NAMBLA.'

Spike TV (now Paramount Network) planned a second season in August 2004, but production stopped due to Krucfalusi's continued inability to meet his deadlines.

Billy West said in an interview that he did not wish to voice Stimpy in the Adult Party Cartoon because he believed that the series was not funny and that voicing Stimpy in it would damage his career.

Aside from Mr. Horse, most of the main supporting characters such as Powdered Toastman, George Liquor, and Muddy Mudskipper do not return for the revival.