Ear Worm: "Dancing in the Moonlight" from The Next Steps, a.k.a. "Slumber Party Song." You can watch the official music video from the Angelina YouTube feed here.
Playing Against Type: An in-universe example in the 2002 episode "The Show Must Go On" - in a special Christmas production of Cinderella, the usually sweet Angelina is cast as the Wicked Stepmother (or "Stepmouse" as called on the show) while Priscilla Pinkpaws gets cast as Cinderella.
Wild Card: Sammy Watts. Sometimes Sammy liked to cause trouble on his own, other times he'd join the Pinkpaw twins in troublemaking, and a few times, he actually helps out Angelina and friends!