Sets released: Mirrodin Besieged, New Phyrexia

Major stuff:

   - New Phyrexia introduced Phyrexian mana costs {W/P}, {U/P}, {B/P},
     {R/P} and {G/P}.  These costs may be paid with one mana of the
     appropriate color or by paying 2 life.

Minor stuff:

   - Mirrodin Besieged brings battle cry and living weapon.
   - New Phyrexia brings
   - The rules on poison in the two-headed giant format were adjusted
     to create a shared poison tally that can get up to 15 before the
     team loses.
   - Mirrodin Besieged has the first card in it to restart the game and
     a cycle of cards that trigger when revealed from a player's opening
     hand.