Hedron Fields of Agadeem

Oracle Text

Creatures with power 7 or greater can't attack or block.

Whenever you roll H, create a 7/7 colorless Eldrazi creature token with annihilator 1. (Whenever it attacks, defending player sacrifices a permanent.)

Card Rulings

6/1/2012 A creature’s power is checked when attackers or blockers are declared. Increasing the power of an attacking or blocking creature to 7 or greater won’t remove that creature from combat.