The Mets have now lost 386 games by walk-off, including postseason. 7 of them have been by walk-off grand slam. Do you really want to know any more than that?
A blog devoted to cataloguing New York Mets walk-offs and other trivia. For those unaware of the definition of walk-off just replace the term with the words "game-ending" and you should have a much better understanding of the phrase.