Metal Slug XX is basically an enhanced version of Metal Slug 7, released in North America for the Nintendo DS and Sony PSP in November of 2008, but it includes some extra content not found in the previous iterations.
'Combat School,' a compilation of over seventy mission-based trials, encourages players to compete for the best scores, and cooperative multiplayer also makes an appearance. In addition to the six playable characters included in the game, fans will also be able to download a seventh, named Leona, from the PlayStation Store. She's only $0.99!
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The blog is also running a couple of related give-aways for Metal Slug stuff, including four pairs of "nifty Metal Slug boxers" which are "not quite for wearing," and nine Japanese promotional posters for the game. Interested swag-seekers simply need to post a comment in the blog post explaining their favorite aspect of Metal Slug (free registration required).