Keep Circulating the Tapes: the only official DVD releases this series got were 3 single disc sets containing 3 episodes each, which doesn't even comprise the whole first season, though a first season set has been made but good luck finding it. A second season DVD set has been released but it's out of print and a bit pricy. Fortunately the entire series is on Neflix and Hulu and can be purchased off of iTunes.
The Other Darrin: When Hak Foo originally debuted in the first season episode "The Dog & Piggy Show", he was voiced by Jim Cummings. After he became a regular, starting with season 2, John DiMaggio took over the role. In "Deja Vu", when Jackie relives the events of Hak's debut episode DiMaggio still voices the character.
Likewise, as stated in the Hey, It's That Voice! entry above, Julian Sands voiced Valmont, but only for seasons 1 & 2. Greg Ellis voiced him in season 3 and Andrew Abselon voiced his handful of appearances in season 4.
Real-Life Relative: Stacie Chan, who voices Jackie's niece Jade in the cartoon and asks him questions from kids at the end of each episode, is in fact Jackie Chan's niece in real life.
Recycled Script: They even lampshade it. Season One had the team looking for the 12 talismans of Shendu and Season Two had them trying to prevent the unsealing of the 8 demon sorcerers. Season Three had the talismans destroyed and inhabit the animal namesake (the same magic in a new container) and season five had them looking for the artifacts of the immortals that imprisoned the 8 demon sorcerers (same elemental powers in new containers). Season four is the only completely original season with the Shadowkhan masks.
The entire main plot arcs of all five seasons follow a basic structure: Locate potentially dangerous, if not apocalyptic, magical power sealed away somewhere around the world.
Drago evaluating potential henchmen when looking for people to replace the Enforcers. The rejects (other than Valmont) showed results similar to those from when Finn tried to create his own gang.