(at around 38 mins) When Lee's appearance is turned from being a 'Nothing-Face' into the Playboy centerfold model, a staple, although oversized, also materializes on Lee since it was visible when the picture of the centerfold was looked at, but when Lee's appearance changes from that of the model into the Hungry Heifer Manager (at around 50 mins), glasses do not materialize on Lee's face, even though the restaurant manager was wearing glasses at that time.
One of the Crites bites the truck tire and fills itself full of air, Yet the tire never goes flat and no one changes the tire for the remainder of the movie.
(at around 33 mins) During the close up shot of the dead sheriff in the Easter Bunny costume at the church, you can clearly see the zip of the costume is done up yet in the scene before it was stuck hence how the critters got inside the suit.
(at around 1h 8 mins) When the Critters are rolling together to the Polar Ice Burger, you can see in several shots that the furry balls are connected together to some device pulling them all along (there are often visible wires).
Throughout the movie whenever the critters roll, you can see the wires pulling them.
Near the end of the film, as Charlie and Uf face one another (both played by the same actor), and circle around, they are clearly matted into the shot, as they are both semi-transparent. This is most obvious when the bus' mirror is visible through their heads.
When Brad looks at the picture of him and Charlie, it's an obvious still shot from the first movie.