The effect "Afflicts your attacker with deadly poison spores each time you block." causes a stacking debuff to anything whose attack the player blocks. This debuff stacks to 5, starting at 12 nature damage every 3 seconds and stacking to 60 nature damage every 3 seconds. Does not appear to be affected by +Spell Damage effects. This is an excellent shield for a Protection Pally to AoE grind with.