Doug Takes a Hike / Doug Rocks - S1-E4
Continuity mistake: When Roger is dancing in Skeeter's yard, he changes color.
Doug to the Rescue / Doug's Cool Shoes - S1-E7
Continuity mistake: Doug's Cool Shoes: When Doug is buying shoes, the saleslady takes off Doug's sneaker and when it shows the shoebox, his other shoe is already in there.
Continuity mistake: Patti sings terribly in this episode. But in "Doug's No Dummy", she could sing perfectly.
Suggested correction: While it is shocking, one thing to consider is Patti is going through puberty. It's not just boys who need to relearn how to sing with puberty and can go from canaries to frogs; girls do too. Especially if they have not had proper training, and are aiming for notes they can no longer hit. Patti's at the right age. She may be going through the same thing.
Doug's Halloween Adventure - S4-E12
Continuity mistake: Skeeter, Doug, and Roger are all in line for the scary ride. There are a lot of people behind them. The park closes and the people behind them instantly disappear in a cut.
Doug is Quailman / Doug Out in Left Field - S1-E12
Continuity mistake: The baseball players on Patty's team appear out of nowhere near the beginning. She walks back to the bench in defeat and it's just Doug and Skeeter. A couple of seconds later there are a lot of people in the stands.
Doug's Cartoon / Doug's Monster Movie - S3-E8
Continuity mistake: There is a person holding a sign next to Judy. It says "No censorship." This sign changes. The word spacing is different in the closer angle. In the wide angle there is a noticeable space between the word censor and ship.
Doug to the Rescue / Doug's Cool Shoes - S1-E7
Continuity mistake: Patty's notebook disappears and reappears when she is being bothered by Roger in detention.
Continuity mistake: Patty's hair changes color many times throughout the episode. In some cases it's lighter, in other cases it's the normal color.
Doug's Servitude / Doug Rocks the House - S3-E2
Continuity mistake: Doug is building a house out of playing cards at the end. He has a deck next to him he's using. When porkchop destroys the house, the deck of cards disappears.