Terrence Mann's appearance as Ug is credited in the movie's end credits before he has even appeared in the movie. He only makes a short appearance in a scene running during the end credits, which ties the actions of this movie with the sequel Critters 4 (1992).
Leonardo DiCaprio has commented on this film stating: "I admit I've done a few lousy roles in the beginning of my career, like my role in 'Critters 3'. But at that age, you'll do anything for attention!".
Cary Elwes turned down the role of Josh.