Tree House of Horror II: A Simpsons Halloween - S3-E7
Continuity mistake: When Jimbo and Kearney take Homer's candy, it is obviously night time. However if you watch the outside as Homer closes the door before he says "Lousy punks" it shows a daytime sky.
Tree House of Horror II: A Simpsons Halloween - S3-E7
Audio problem: When Kang and Kodos land in Springfield and hit Mayor Quimby with a club, one of them says something but his mouth is not moving.
Tree House of Horror II: A Simpsons Halloween - S3-E7
Continuity mistake: When Mr. Burns is telling the robot Homer that he is his daddy, Burns is to the right of Homer, but after the POV of Burns' face (he is still oriented right of Homer) by Homer, Burns is now to the left of Homer.
Tree House of Horror II: A Simpsons Halloween - S3-E7
Other mistake: As Kang and Kodos fly away from Earth in their spaceship, you can see that the Earth has been coloured wrong. The continents are blue, and the sea is green.