Sets released: Darksteel, Fifth Dawn, Unhinged, Champions of Kamigawa

Major stuff:

   - Darksteel introduced 'indestructible'.
   - Fifth Dawn introduced a darker artifact frame to help distinguish
   artifact cards from white cards.
   - Champions of Kamigawa introduced a new Legend rule (if Legends share
   a name, they are all put into their owners' graveyards, not just all
   but the first) and removed the Legend creature type, creating 'Legendary
   Creature'.
   - Champions of Kamigawa introduced flip cards, cards with a compressed
   card face on either end and a suitable picture in the middle.
   - Champions of Kamigawa introduced a modification to the targeting rule
   (targets only need to be unique for each instance of the qualifier
   'target') to assist with splice cards.
   - Champions of Kamigawa introduced the 'defender' ability, retroactively
   added to all of the creatures with creature type Wall, to eliminate
   the direct link between creature type and not being able to attack.