Something I put together, hope you all enjoy:
When you break the chains binding the cursed sword Fang of Night and draw it in battle, deal an extra +2d6 whenever you deal damage. When the battle ends, roll +cha. On a 10+ you can resist the sword's pull, but not forever: the next time you would use this move, take a -1 penalty to your roll (stacks cumulatively). On a 7-9, choose choose one:.
-Your victory is hollow, either putting you in a worse situation than you were in before or somehow harming someone or something important to you.
-The Fang of Night's thirst for blood is unsatisfied by your paltry offering; end the life of a surrendered opponent or lose half your hitpoints, rounded up.
-The Fang of Night draws upon your life force; permanently lose a stat point (GM's choice) until the next time you draw it.
On a miss, the GM describes how the cursed sword's powers run amok.
Cursed Knight
When you become corrupted by the Fang of Night, you must take the following move in place of your next advance.
Chosen: The Fang of Night becomes permanently bonded to you. Any favored weapon bonuses you have are applied to the Fang of Night, and you can call it to your hand at will. You do not use the above move when attacking, and instead deal +1d6 whenever you deal damage. You gain an obvious and difficult to conceal mark of corruption.
In addition, you can gain the following moves on level up:
By Blood Sustained: Whenever you deal damage with the Fang of Night, gain +1d8 hit points. You can no longer regain hit through any other method including resting or healing magic. Lose 1 hit point every 24 hours in which the Fang of Night does not taste blood.
Unchain the Beast: When you draw deeply on the power of the Fang of Night, roll +cha. Your bonus from Chosen temporarily increases to 2d6. On a 10+, you are able to maintain complete control. On a 6-9, choose one. On a miss, GM chooses one.
-You attack the nearest living thing
-You lose 1d6 hit points
-Your armor is temporarily halved (rounded down)
Undying Hunger: As long as you are either dealing damage or moving directly towards a target within sight range with the intent to do so, you cannot die. If you are at 0 hit points or less and do not meet this condition, immediately take a Last Breath. If you fail this roll, your physical body disintegrates into shadow and you become a thrall of the Fang of Night.