Danny Phantom - Season 2 Episode 14 Masters of All Time

Vlad is back, only now he's afflicted with a serious case of ecto-acne, a direct result of the college lab accident with Jack and Maddie. To ensure Danny helps him find a cure, Vlad infects Sam and Tucker with his disease, and Danny turns to Clockwork for help. Danny convinces Clockwork to let him go back in time to make sure the accident that injures Vlad never happens. Unfortunately, when he changes the past, he changes the present. When he arrives back in the present day, Maddie is married to Vlad and living in Wisconsin, and Jack's a ghost named Jack Plasmius! Now, Danny must go back in time for a second time to ensure his parents get together, but when he does, will that mean ecto-acne doom for Tucker and Sam?