The Other Darrin: After Bill Scott passed away, Corey Burton voiced Gruffi for the rest of the series. Also, Paul Winchell left the series after Season Five, so Jim Cummings took over as the voice of Zummi.
Also, the voice artist for Cavin has changed regularly during the course of the show's run as the artist in question grew up and his voice broke and had to be replaced. In this case, Christian Jacobs first voiced Cavin during season 1, then Brett Johnson did the honors in season 2, followed by David Faustino in season 3, then Jason Marsden in seasons 4 and 5, and finally R.J. Williams in season 6.
Talking to Himself: All the way in the Mexican Spanish dub, especially between Sunni and Calla, who are very good friends, albeit it's not too notable because all the voice actors managed to sound too different between each character.