OD&D Martial Art: The Lessening Way
Everybody's Doing It! So now I am too. Blame Nathan for this.
One does not go out seeking martial arts in order to become more humble, more mundane, more normal and human. The people who want to simply live their lives in contentment do so.
The Lessening Way
For the others, the Monks of Nullification offer a solution. If you seek power, there is a cost. If you want to gain, you must lose. If you are to become a monster, you must make yourself Lesser.
Layer I: Cut off one of your arms. Your other arm now strikes as a magical weapon dealing 1d6+2 damage and doubling any to hit bonuses you already have.
Layer II: Remove your eyes. You can now sense everyone within a 20 ft radius of you, including incorporeal, otherworldly or magically hidden beings. You can strike at any of them, they can't hide from you anymore.
Layer III: Remove your heart and replace it with a lump of granite. You are now immune to all emotion-based magic, mind control and fear. Once a day you may kill a man through the sheer power of your contempt for life. They get a saving throw to resist.
Layer IV: Cut off your own head. Ascend into power and cause murder and devastation for 1 hour, causing 6d6 damage per hit and being able to hit everyone you can perceive at once with the same attack. Then you die. The world is better off for it.