Vanguard is a special card type and a extra you could add to any game if you just have 1 of these cards for each player.
Vanguards affect how many cards you draw at beginning of the game how big is your maximum hand size and your starting life total.
Vanguards each have a special ability that you can use during the game.
Vanguards are not considered cards in game so they cannot be affected by other cards.
MTG blog 