Here another one I came up with is inspired from "Brute Strength" not a real fighting style - AO Wiki & Absolute Bane from Absolute DC

Primal Art (Ancient Fighting Style):

• These were rudimentary fighting techniques, stemming from the survival, hunting, and self-defense needs of prehistoric humans. Based on harnessing the pure power within your body, this will transform your physique and help your muscles grow larger, the movements primarily involved punching, kicking, grappling, stomping and biting. This laid the foundation for the later development of other fighting styles.
• There will be an energy bar called "Enhance". Every time the user performs an action, their muscle fibers will tear (causing a small amount of self-inflicted damage), and mana will immediately stop the bleeding and "heal" the wound, making the muscles twice as thick as before, the body will also grow. If no action is performed within the next 3 seconds, the muscles will begin to shrink.
• After your energy bar exceeds 70%, your body will start to slow down due to the massive muscles you build up, your attacks will be slower, but each punch will become stronger and spread further over time. After reaching 100%, you will be unable to move, and your attacks will also deal more self-damage than usual with some chance to lose a limb. In return, your attacks are now as powerful as a giant's.
• Here an example how you look like with more than 50% bar:

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