Core:Block Interaction

If an attack hits, but has not gone critical, then the defender has a chance to block. In addition to the AV of armor, every other item has some block value (BV). If the defender attempts an ability that uses the block interaction, then they add the item's BV to their armor class. If the new total is greater than the attacker's attack roll, then the block succeeds. If the new total is less than or equal to the attacker's attack roll, then the block fails. The consequence of a successful or unsuccessful block are described in the "On success" and "On fail" section of the ability that's used. For a Basic Block, a successful block causes the attacking effect to fizzle.

Every time you block with the same item in the same turn, its BV is reduced by 1 (to a minimum of 0). This is referred to as the item's block penalty. blocking items do not suffer this penalty.