Resilient Endurance [Armor, Power]

You constantly put yourself through grueling trials of endurance, never resting until you can withstand what would lay most men on their deathbed. Your devotion to your stamina brings many benefits.

Base Mastery 1:

Prereq: Power or two-handed weapon

You may apply your Constitution modifier instead of your Strength modifier on attack rolls, holding your weapon in powerful but draining stances that lesser warriors cannot maintain.

Expanded Mastery 2:

Your extended training leaves you able to refuse the effects of fatigue and exhaustion, pushing yourself far past the limits of what is considered normal. You gain a +10 bonus on the following checks and saves: Swim checks made to resist nonlethal damage, Con checks made to continue running, Con checks made to avoid nonlethal damage from a forced march, Con checks made to hold your breath, Con checks made to avoid nonlethal damage from starvation or thirst, Fort saves made to avoid nonlethal damage from hot or cold environments, Fort saves made to resist damage from suffocation, and Fort saves made to resist effects that would make you fatigued. As well, if you would be fatigued without a save (such as by sleeping in heavy armor), you may avoid the fatigue by succeeding at a Fort Save DC 30 (you gain the +10 bonus on this roll). The effects of the Endurance feat stack with this feat.

Expanded Mastery 3:

You may ignore lesser pains caused by harsh environments. You can ignore 1 point of damage per round from ongoing damaging environmental effects. This includes damage from exposure in the hot desert, but not damage from directed attacks, like a fire-based battlespell.

Expanded Mastery 4:

You refuse pain, inuring yourself against damage. You gain 1d4 DR. This DR is treated as armor, and bonuses from effects such as Armor Mastery apply to it. You may only benefit from a single source of armor DR at a time, however - you only make a single DR roll using the greatest DR source if you have this feat and wear armor at the same time.

Expanded Mastery 5:

You put the full power of your fortitude behind your strikes, battering aside an opponent's defenses with relentless strikes. You may apply your Constitution modifier to damage, instead of your Strength modifier.

Expanded Mastery 6:

Banishing all weakness from your body, you refuse to allow pathogens a foothold. You gain a +10 on all saves against poison, disease, or ability damage.

Expanded Mastery 7:

With concentration, you may ignore much greater ongoing pains. If you study a given situation, environment, or area for 1 round, you can ignore any circumstance penalties placed on attack and damage rolls, checks, and saves due to the conditions of that area for the next 10 rounds. For example, after summoning your strength for 1 round, you may attack underwater without penalty. As well, you may ignore up to 10 point of damage per round from damaging environmental affects. This includes damage from running through a burning building, but not damage from directed attacks such as a fire elemental's burning attack. This stacks with the ability to ignore damage granted by EM3.

Expanded Mastery 8:

Your training allows you to refuse nearly any debilitating effect. You gain a +10 on saves against blinding attacks, deafening attacks, paralysis, stunning, nausea, and daze effects, and ability drain.

Expanded Mastery 9:

Your ability to banish distraction and pain is legendary. Reduce all circumstance penalties to attack and damage rolls, checks, and saves by 4. As well, you can ignore up to 10 points of damage per round from ongoing damaging effects constantly. This includes damage from crossing a frozen tundra without winter gear, but not damage from directed attacks, such as a dragon's breath attack. This stacks with the ability to ignore damage granted by EMs 3 and 7.

Expanded Mastery 10:

You can hang onto the very precipice of death itself, refusing to stop even when dealt mortal wounds. When you are hit by an attack that would reduce you to 0 or fewer hit points, you can make a base attack check (DC equal to the damage dealt). If your check succeeds, you take no damage from the attack — your instincts allow you to turn the blow aside at the last minute. You can use this feat once per encounter. You can only use this feat to evade the damage from a weapon or other blow, not a spell or special ability. You cannot use this feat if you are stunned or helpless.

Thanks to Monte Cook for writing the Oathsworn, from which I blatantly stole several abilities, and to Hong Ooi, from who's Champion of Battle mastery I stole EM10.

Conversion Notes

To convert IH masteries to D&D feats, simply find some level-based progression to hook them off of. Then, assign prereqs such that a specialized character could meet them at a level of (2 * Mastery level) - 1. So a Mastery 5 ability should be accessible at level 9.

For this mastery, BAB prereqs are appropriate, but even more appropriate would be a Fort save based prereq. BM is available at Fort +2, and with each EM available at a Fort save of (mastery level + 1). That's earlier than the standard rules by a level, but it should be just fine.