War Cadence
About this card
War Cadence is an enchantment card in Magic: The Gathering with mana value 3 (color identity: red). First printed in Mercadian Masques (1999); 2 paper printings in total. Legal in Commander, Legacy and Vintage. Cheapest printing: €0.35 (Commander 2013); most expensive: €0.52 (Mercadian Masques).
War Cadence 

The rhythm isn't a call to arms, but a signal that the goblins have made a new enemy.
Name in each language
Legality
Rulings
2004-10-04
The ability only applies to blocks declared after it resolves. It will not add costs to any blockers already announced.
2004-10-04
You can choose X=0. This doesn’t have an effect most of the time, but it does mean that creatures can’t block unless the controller chooses to pay the cost (a cost of zero is not automatically paid). You can use this to make your creatures unable to block an attacker.

