Flying Frog is a dangerous psychpopath who used to be a jester from Mercia.  However, due to his violent rampages amongst the villagers, he was put in prison, but managed to escape and presumably killed his prison guard during the process.  Later on in the years, he became one of the Fearsome Four lead by Mammoth Mogul and eventually the Destructix under many criminals against the Freedom Fighters.  But, since Lightning Lynx's absence, he and the other two remaining members haven't been the same.  Under Fiona's leadership, he and the others team up with Sonic and the Freedom Fighters to bring Lightning back from the Raiju Clan.

When I first came upon Flying Frog, I was given the impression that his personality is a combination of two traits: the psychoticness of the Joker and the goofiness of Pinky from Pinky and the Brain.  Basically, I want a higher tone to match his goofy personality, but nothing too high pitched to make his craziness stand out.