Source: City of Splendors: Waterdeep
You have sacrificed your right hand to Tyr, the Maimed God, proving your resilience and strength of spirit. Most who take this feat wrap their right hands in white gauze, voluntarily refraining from using the hand. Others have lost their hand in battle, and a few fanatical followers of the Maimed God choose to cut off their hand to demonstrate their zeal and devotion to Tyr's faith.
Prerequisite: Patron Tyr, alignment lawful good, ability to turn undead.
Benefit: As long as you refrain from using your tight hand, you receive a +1 sacred bonus on attack rolls, damage rolls, and Will saves.
Since you are using only one hand, you cannot fight with two weapons, wield a two-handed weapon, or fight with a one-handed weapon and a heavy shield. You cam fight with a one-handed weapon and a light shield, but you cannot use your shield hand to hold other objects such as a holy symbol; spell components, or a light source. (This means you must use your weapon hand to cast spells, so you might have to drop or sheathe a weapon when you wish to cast a spell requiring your holy symbol or somatic components.) You take a -4 penalty on Climb, Disable Device, Open Lock, and Tumble checks. You can only gain the benefit of wearing one magic ring.
(If you previously considered yourself right-handed, you suffer no penalty for using your left hand as your primary hand. Handedness isn't defined in the game; the point of the vow is to restrict yourself to using one hand.)
Special: If you violate your oaths and use your right hand for any purpose, you lose the benefits of this feat until you perform a rite of purification in a shrine or temple of Tyr, which requires 24 hours of vigil and prayer.