A comment is made about Marvel "not returning our calls." Characters from the Marvel Universe are conspicuously absent from the Lego movies, due to rights issues with Disney. Characters from the Star Wars universe (also owned by Disney) appeared in La Grande Aventure Lego (2014), but not in this sequel.
Actress Stephanie Beatriz (Sweet Mayhem) has a signature small scar on her right eyebrow which was caused by, coincidentally enough, tripping on a piece of LEGO when she was 10 years old.
During the "Gotham City Guys" song, references are made to every actor who has played Batman in live action movies since 1966: Christian Bale, Michael Keaton, Ben Affleck, George Clooney, Val Kilmer, and Adam West.
Due to the film's box office reception, considered disappointing by the studio's standards, Warner Bros. chose to let their hold on the Lego brand's film rights lapse. Universal Studios subsequently gained the film rights, thus making this the last Lego-based film produced by Warner Bros.
Rex's design was partially inspired by Lego's Jack Stone. Jack Stone was an early 2000s line designed to be hip and edgy, and was widely despised by Lego enthusiasts. In fact, Lego actually uses Jack Stone sets as a teaching example of what NOT to do when designing a new Lego product.