Back in the day, every Pixar movie was accompanied, during the closing credits, with a series of "bloopers." These freshly animated pieces, either combining real in-the-recording-studio bloopers with new animation or wholly invented comedy bits, pushed the metatextual realism to wacky new heights (see the bugs from "A Bug's Life" are actors making a movie!), with some of the outtakes working better than others (my personal favorite are the ones from "Monsters Inc."). Pixar discontinued the bloopers a few movies ago, citing their reluctance to ever fall into a "predictable" pattern (and they would seem horribly out of place on something like "Up" or "Brave"), but it makes sense that "The Lego Movie" would carry that idea forward, with a wonderful blooper reel just as charming and hilarious as the actual movie.
To give away the outtakes would be a punishable offense, but I'll just say that they seem to follow the Pixar formula -- incorporating recording booth screw-ups with comedy bits that the creative team has invented specifically for this reel (you'll even see Lego-ized versions of the directorial team of Phil Lord and Chris Miller). If you loved the movie (and, judging by the box office, there are a lot of you that did) -- you'll love this reel. (Yes, it turns out that Will Arnett's Batman is a real cut up.)
f you haven't seen "The Lego Movie," please go out and see it now. It's probably the first great studio movie of the year and is an absolute hoot. Afterwards, come back and watch the blooper reel. It'll be waiting for you.