Lego Batman: Legacy of the Dark Knight is one of my favorite games of the year so far, and ever since I rolled credits, I’ve been eager to play the DLC. Announced prior to the game’s launch, we knew it would focus on Harley Quinn and the Joker, and today, WB Games has pulled back the curtain on the new content. The new trailer includes gameplay, new suits for the Bat-family, and a release date: September 18. Check out the…