Balloon artist John Reid built this enormous balloon sculpture for the Salt Lake City Comic Con. I cannot verify his claim, but he says that it's the largest balloon sculpture ever built by a single person.
-via Nerd Approved
UPDATE 4/28/14: The Deseret News has more information. Although Guinness World Records has not conferred a record upon Reid, proper record observers were on hand to watch Reid. A time-lapse video that Reid made will help him secure a Guinness record.
The sculpture is 50 feet tall and made of 4,302 balloons. It's so large that it can't stand in the convention center upright. Building it took Reid 42 hours.