Concentrated Warfare

Once per turn at the start of your combat phase
you may tap three or more of your creatures to
target one of defending player's lands. Defending
player reveals the top card of his or her library (if
the targeted land is a non-basic land, defending
player instead reveals the top two cards of his or
her library). If the revealed cards' combined
mana cost is less than the number of creatures
you have attacking the target land, target land is
destroyed. Defending player shuffles the revealed