Ambush Bug is easily one of the most obscure characters in the DC Comics universe. To date, he's only appeared in one TV show, and as a "reporter" during the early days of the New 52 comics as they "teased" upcoming issues of certain comics.
Arguably though, his greatest apperance was in the series finale of Batman The Brave and The Bold. Where he fought to keep the show on the air, as Bat-Mite tried to get it cancelled. As a being of the "fifth dimension" he had not only knowledge of the show's world and our world, but was able to travel to them and be where he needed to be.
In the end, his efforts were in vain. But, because of his abilities, he was able to get the cast together for a send that is truly amazing.
Oh, and he was voiced by Henry Winkler, can't top that.