If you didn't experience it last year and you're an Xbox Live Gold member, you can rectify that by acquiring Battleblock Theater at no extra cost. The game's just replaced Gotham City Impostors on Xbox's Games with Gold program, and so it'll stay free to Gold members until the end of the month. To grab it, head on over to the Xbox Games Store.
In a case of artful timing, dev The Behemoth just launched its Arena Mode Playlist Creation Contest for Xbox and Steam players. Arty types can submit arena level creations between now and August 15, and the best playlists will win signed Battleblock Theater merchandise, as well as, in the words of The Behemoth, "immediate and exciting recognition as an Arena Mode Feature in-game." For more details, point your fingercursors here.