"The Cat & Birdy Warneroonie Pinky Brainy Big Cartoonie Show" was a show that began airing on Kids' WB!'s Saturday morning lineup on January 10, 1999. Originally airing for an hour and a half (with "Histeria!" making up the last half-hour of the schedule), "The Big Cartoonie Show" followed a similar format to many "Looney Tunes" compilation shows of the past, but also included segments from "Tiny Toon Adventures", "Animaniacs", "Pinky and the Brain" (and "Pinky, Elmyra and the Brain"), and "The Sylvester & Tweety Mysteries". (Essentially, you could think of it as an attempt to keep "Animaniacs" on the Saturday morning schedule despite the fact that it was now cancelled.) But after four episodes in that form, Kids' WB! began airing a certain Japanese-created video game-based cartoon that shall remain nameless, and as a result, "The Big Cartoonie Show" was cut down to just half an hour and showed only segments from "Animaniacs" and "Pinky, Elmyra and the Brain" (although it should be noted that most episodes from the latter series were first shown here).
This is actually the second of four intro sequences I know that the show had, three of them in the first season alone. The first one had the "Looney Tunes" characters singing the song alongside the "Animaniacs" characters, then it was replaced with this one where the only "Looney Tunes" character who appears is Michigan J. Frog. Two episodes ran with a shortened version where they cut to "It's got cheese and pepperooni!" right after "'Cause this name is not so puny", which was sung by Brain instead of Slappy in that version.