The 2nd expansion was released on 16 March 2010 which raises the number of sideboard cards per deck to 23.
If you unlock the full set of cards for 3 decks, you earn a Planeswalker T-shirt for your Xbox Avatar. If you unlock the full set of cards for 6 decks altogether, you earn a MTG deck prop for your Avatar.
Here’s a short video of my Avatar wearing the T-shirt and equipped with the MTG deck prop.
I also took some pictures of the new cards in the new expansion.