The scenes also required another set of skills, drawing on Lord and Miller's background directing the live-action "21 Jump Street" and the movie's upcoming sequel, in addition to their animation bona fides on the animated franchise "Cloudy With a Chance of Meatballs."

Even after production wrapped, the ending presented challenges. Producer Dan Lin noted the task of keeping it a surprise during promotional efforts — not easy in a world where blog posts can reveal a movie's intimate plot points and social-media can carry them around the world with blazing speed.

Though the main coup comes with the suggestion that the film was the product of someone's imagination, filmmakers couldn't resist other wrinkles. They hinted, for instance at a sequel by introducing the idea of Finn's sister, who loves the younger-skewing toy Duplo, also made by Lego.)

PHOTOS: Billion-dollar movie club

Adding to the father-son theme, the voice of Finn's sister is played by Miller's own son, his high voice at the time sounding a bit more girlish.

So are Lord and Miller happy with the meta-universe they created? "What we kind of wanted to go for throughout the movie was ask questions about why characters are behaving this way," Lord said. "We spent a lot of time trying to figure out the right tone and level of magic, whether there really is a Lego universe where toys are alive or it's just someone's imagination. So yes. I think so." He paused. "I hope so."