Scott Pilgrim vs. The World is getting online multiplayer on 19th August on XBLA.
That's over two years since the release of the nostalgia-rich beat-'em-up parent game, which celebrates it's second anniversary on 10th August.
The long overdue DLC was quietly announced on Major Nelson's Blog
hidden among several other release dates. The listing simply stated "Scott Pilgrim: Online Multiplayer + Wallace Pack," so i'd assume you'll get to play as Scott's snarky gay roommate Wallace.
No official announcement has been made for a PSN release but will update you guys if things change.