Here is the cards in the combo:
Unnatural Selection:
1U Enchantment
1: Choose a creature type other than wall.  Target creature's creature type becomes that type until end of turn.
The flagbearer ability is:
If a spell or ability an opponent controls could target a Flagbearer in play, that player chooses at least one Flagbearer as a target.
The idea is to change a creature's type to flagbearer so that any spell that targets one of your creatures (like Shock) is transferred to one of your opponent's creatures.
There is a slight problem: The Flagbearer's ability that makes you target a flagbearer isn't actually part of the creature type.  So if you change a creature's type to flabearer, and no other "real flagbearers" (like Standard Bearer or Coalition Honor Guard) are in play, then the player may target anything he or she chooses.  This is also on the Apocalypse FAQ at the Wizards website at
-Ronald C.