Pierce X (Weapon Keyword)
If an attacking unit attacks with a weapon with the Pierce X keyword it may cancel up to X
results during the Modify Defense Dice step.The Pierce X keyword can be used to cancel results on defense dice rolled by a unit using the Guardian X keyword. When doing so, treat canceled results as blank results. After using the Pierce X keyword in this way, any unused Pierce X value can still be used to cancel results rolled by the defending unit.For example, a unit with Pierce 3 attacks an enemy unit, and another enemy unit uses Guardian 2 to cancel 2 hit 
results. After converting defense surge 
results, the unit using Guardian has rolled 2 block results. The attacking unit uses Pierce to cancel the 2 block results and the unit using Guardian suffers 2 wounds.Now the defending unit rolls defense dice and the attacking unit may cancel 1 more block result rolled by the defending unit since only 2 of its original Pierce 3 have been used so far.
results. After converting defense surge results, the unit using Guardian has rolled 2 block results. The attacking unit uses Pierce to cancel the 2 block results and the unit using Guardian suffers 2 wounds.Now the defending unit rolls defense dice and the attacking unit may cancel 1 more block result rolled by the defending unit since only 2 of its original Pierce 3 have been used so far.