Resilience, Toughness or another term.
Counter the effects of Pierce Defense + Pierce Magic Defense.
Does NOT add additional defense or Damage Reduction, simply reduces the effectiveness of Piercing Statistics.
Why?
Because I hate improperly balanced statistics and, I don't think having statistics that cannot be countered is imbalanced.
Additional Request:
Trinkets, Amulets etc.
New equipment slot with various effects.
Examples:
Raider Singet of Impacts: Usage of this item instantly adds max stacks of Critical Impact
Item CD: 60 seconds
Amulet of Arua:
Instantly remove all stacks of healing reduction on yourself.
Item CD: 45 seconds
Totem of Solid Stance:
Using this item will grant you 30% stun resistance and 60% sleep resistance for 15 seconds.
Item CD: 60 seconds
etc.
The trinkets are orientated [idealy] towards managing harmful or beneficial 'stacks' [the temporary skill/status next to the mini map]. They add no other statistical advantages.