You equate pain with discipline and can inflict damage upon yourself to unlock greater power.
Benefit(s): During your hour-long reckoning, if you choose to deal lethal damage to yourself, you reach a state of fantastic focus. Once during the next 24 hours, you can draw upon this focus to gain the benefits of any one of the following effects. To activate the ability, you must deal 1 point of lethal damage to yourself as a swift action (unless otherwise noted). Members of the Order of the Nail often install a sharp barb within their armor that deals this damage when the wearer is subject to a critical hit; if you’re struck by a critical hit while wearing such armor, using this ability doesn’t require a swift action.
Fervor: The DCs to resist the effects of the boons granted by your Hell Knight Obedience feat increase by 1 for 1 hour.
Indomitability: You can reroll a single failed Will saving throw and must take the result of the second roll, even if it is worse. A swift action isn’t required to use this effect, but you must still take 1 point of damage.
Mercilessness: The critical threat range of your order’s favored weapon doubles for 1 hour (even if it is not a piercing or slashing weapon). This does not stack with any other effects that increase a weapon’s critical threat range.
Pathfinder Campaign Setting: Path of the Hellknight © 2016, Paizo Inc.; Author: F. Wesley Schneider.