I was flicking through channels when I saw an episode of Duck Dodgers that was starring Dave Mustaine! Did someone fake Dave's voice or is that actually Dave's voice?
No, you were not just hearing things. That was indeed the voice of Dave Mustaine, starring as himself. The episode of Duck Dodgers you are referring to is called "In Space, No-one Can Hear You Rock/Ridealong Calamity". It originally aired Saturday, November 5, 2005 on the Cartoon/Boomerang Network. In this episode, the Martians create a weapon to drain energy from Earth's music and use its atomic power to destroy the Earth. Dodgers unfreezes Dave to play enough heavy metal to overload the device. Megaduck rules! Now I've always known Dave was a rock star, but to save the planet as well? My hat is off to you sir!
Duck Dodgers was not Mustaine's only television appearance. He has also been featured on Rock N Roll Jeopardy!,The Drew Carrey Show, Black Scorpion, Behind the Music, I Love the 80s, Never Mind the Buzzcocks, Top Ten, Headbanger's Ball, CNN, and several others. Seems he's had quite the TV career!