Fortitude works similar to adrenaline or energy in that it provides necessary fuel to use certain skills.
However, unlike energy or adrenaline, fortitude increases by one everytime you take a hit of damage from any source (excluding sacrifice health). The amount of damage is irrelevant.
The types of skills utilizing fortitude should be largely defensive in nature, being a contrast to adrenaline which largely utilizes attack skills.
Some examples:
Iron Will - (8 fortitude, 1 sec cast, 30 recharge) Stance. For 5...12 seconds, the next 3 hits dealt to you are reduced by 10...50%. For each hit taken in this way, you lose 3 energy or Iron Will ends.
Perseverance - (4 fortitude, 1 sec cast, 20 recharge) Stance. For 10 seconds, the next time you are hit with a physical attack, the damage is negated, and you gain energy equal to that damage divided by 50...10.
Self-inflicted Wound - (6 fortitude, 1 sec cast, 20 recharge) Stance. You begin bleeding for 10 seconds and andrenaline gained is doubled.
Zeal - (5 fortitude, 1 sec cast, 20 recharge) Elite stance. For 5..12 seconds, you attack 20% faster and for each strike of fortitude gained, you gain one strike of adrenaline.
Dwayna's Mercy - (8 fortitude, 1 sec cast, 30 recharge) Elite stance. For 8 seconds, your attacks deal no damage. Instead, you are healed for the damage that would have been inflicted to target foe.
Passion - (5 fortitude, 1 sec cast, 20 recharge) Stance. For 20 seconds, if you are knocked down, knockdown duration is reduced to 1/2 second and your next 3 attacks recharge twice as fast.
Defender's Resolve - (7 fortitude, 1 sec cast, 30 recharge) For 10 seconds, you have a 30% chance to block. If you block in this way, you gain 5 energy.
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