A modifier which affects an Armour Saving Throw (Saving Throw Rules) negatively. Each point of Critical Hit Chance allows an attack to act as if it had +1 PEN exclusively for the purposes of dictating whether a Critical Hit has been landed or not.
For example, an attack in which PEN is equal to ARM would conventionally resolve its Armour Saving Throw like this:
- Save on a 4+. Critical Hit on 1.
However, if a +1 Critical Hit Chance is involved, it would be resolved like this:
- Save on a 4+. Critical Hit on 2-.