Creatures can't attack you or a planeswalker you control unless their controller pays
6/1/2011 A card with Phyrexian mana symbols in its mana cost is each color that appears in that mana cost, regardless of how that cost may have been paid.
6/1/2011 To calculate the converted mana cost of a card with Phyrexian mana symbols in its cost, count each Phyrexian mana symbol as 1.
6/1/2011 As you cast a spell or activate an activated ability with one or more Phyrexian mana symbols in its cost, you choose how to pay for each Phyrexian mana symbol at the same time you would choose modes or choose a value for X.
6/1/2011 If you’re at 1 life or less, you can’t pay 2 life.
6/1/2011 Phyrexian mana is not a new color. Players can’t add Phyrexian mana to their mana pools.
6/1/2011 The controller of each creature attacking you or a planeswalker you control pays either or 2 life as attackers are being declared.
6/1/2011 If a player attacks with more than one creature, that player chooses how to pay each cost individually. For example, if you attack with two creatures, you may pay for one cost and 2 life for the other.
6/1/2011 Multiple Norn’s Annexes controlled by the same player will each impose a cost to attack. Players choose how they pay each cost individually. For example, if a creature you control is attacking a player who controls two Norn’s Annexes, you may pay for one cost and 2 life for the other.
6/1/2011 If you control Norn’s Annex, your opponents can choose not to attack with a creature with an ability that says it must attack.