Audio problem: Cruella shows up to buy the puppies. She starts yelling about her pen not working. As she's yelling, her mouth is not moving with what she's saying.
Other mistake: When they are counting the puppies at the end they count the puppies on the stairs. One of the puppies has a red collar, only the original 15 have collars, so this dog is counted twice. So the title of the movie should be 100 dalmatians.
Continuity mistake: When Prissy's owner hears her barking, she pulls her into the house and shuts the window. In the next shot, the window is open again.