Not to be outdone by the brick-and-mortar antics of Wal-Mart, Amazon is offering a $20 credit toward future game purchases for pre-ordering Super Mario Galaxy 2. It's like you're saving money on video games from the future. The news follows the discovery that Wal-Mart is offering the same deal for both Super Mario Galaxy 2 and Halo: Reach. As we reported earlier this morning, Amazon has also countered the Reach offer. With Mario being discounted as well, it's pretty clear that Amazon doesn't want to be undercut on either potential blockbuster.