Character mistake: When Stan inflates himself, Michael asks, "How'd he do that?", implying that he doesn't know the rules of the Looney Tunes world. Since Michael was rolled into a ball by the aliens earlier in the film, this shouldn't be too much of a surprise.
Suggested correction: When Michael was rolled into a ball, he wasn't concerned with how that was possible and soon after he forgot about it. He was more concerned with dealing with the Monstars at the time and, in particular, helping his cartoon friends preparing for the game. When Michael witnessed Stan being flattened and inflated, it looked particularly strange and unfamiliar to him, unlike before as he couldn't watch himself experiencing being rolled into a ball. And that is what triggered his response about questioning how it was possible.
Character mistake: When Nanny is coming home from getting the collars, she calls for Roger and Anita to come downstairs. Plowright accidentally says "Roderick, " rather than "Roger."
Character mistake: When Harry takes the kids to his business, he's showing them how he "restores" cars. After putting the bumper on, Harry says, "Transmission. The sawdust quietens the gears and let's the engine run as sweet as a nut." Putting sawdust into the transmission would not change how the engine runs as they are two separate components. It may make the transmission quieter but would have zero effect on the engine.