Celebrity Voice Actor: Aside from the main cast and cameo characters, there's still plenty of this. Channing Tatum, Will Arnett and Cobie Smulders play Superman, Batman and Wonder Woman respectively. Also Will Forte, Dave Franco, Jake Johnson, Keegan-Michael Key and Jorma Taccone all voice minor characters and various extras.
One of the construction workers and The Man Upstairs are Shrek.
Lying Creator: Before the film's release, LEGO kept telling people that Star Wars characters wouldn't be appearing due to conflicts with Disney. This kept one of the film's best cameos a nice surprise.
The Japanese dub's first trailer had Ichirō Nagai as the voice of Vitruvius. Presumably due to Nagai's death in January of 2014, the role is instead played by Michio Hazama.
The exact same was true for the Hungarian version: early promos featured one of Morgan Freeman's two "regular" dubbing actors (Gábor Reviczky), later ones used the other (László Helyey). With Helyey's death in January, the dub was made using a third actor, who sounded nothing like Freeman. Outside of Wyldstyle, all other character also changed their voices from the promos.
Promoted Fanboy: Most of the cast and crew by nature, but Liam Neeson two-fold. He and his nieces and nephews played with LEGO and he jumped at the chance at a role in the film. He also visibly Squeed a little during an interview when he talked about making jokes with Will Ferrell.
Spoiled By The Merchandise: Bad Cop's "Scribble Face" minifigure revealed his fate in the movie, and while not an exact interpretation of the scenes, the "Lord Business' Evil Lair" playset revealed many details, including Bad Cop's parents frozen by glue and Princess Unikitty in her "business" disguise.
What Could Have Been: The directors couldn't get all the licensed characters they wanted. They haven't said who these were, but obvious absentees various Disney properties including Marvel Universe, Pirates of the Caribbean, and Star Wars. ExceptStar Wars characters did make it into the movie, which was thought otherwise thanks to the creators deliberately misleading the audience in interviews. Of course, LEGO has worked with Star Wars since long before Disney came into the picture.
A script for the old ''Piece of Resistance'' title has surfaced. It's incredibly different from the final version, with many of the character's names changed, R2D2 and Indiana Jones being main characters, Emmet still living with his elderly mother, who turns out to be "the most powerful woman in the universe", had Bad Cop actually swear instead of saying "darn", Larry the Barista having a larger role, and Benny having a co-pilot that's an inanimate mop called Moppy.
The ending credits were meant to be more grandiose with the LEGO bricks spelling out the casts' name in a world that represents them (Unikitty would be in a cutsy world, Batman a Gotham-like city, etc). But the producers found it would take too many LEGO bricks and time to do, as the credits were actual stop-motion rather than CGI like the rest of the film.