Trading deadly blows with your enemies is the absolute greatest pleasure you know. Using your own wounds to motivate and bolster your own retaliatory attacks, not only do you feel comfortable with the pain, you seek it out. As long as you draw breath you can keep up the assault, but the closer you are to the brink, the more enjoyable the encounter becomes.

Blood Fuels Rage

Beginning at 3rd level, the lower your hit points are, the more damage you can deal while raging. If you are below your hit point maximum while raging, your attacks deal an extra 1d4 points of damage, if you are below half it becomes 1d6, and if you are below one-quarter it becomes 1d8.

At higher levels, the extra damage increases. At 10th level, the damage at each tier becomes 2d4, 2d6, and 2d8 respectively. At 14th level, they become 3d4, 3d6, and 3d8.

Masochist

Also at 3rd level, as a bonus action or when you activate rage, you can disable your resistance to bludgeoning, piercing, and slashing damage. You can later re-enable it as a bonus action.

Share the Pain

Starting at 6th level, you can mitigate some of the damage you take and redirect it to the next creature you hit. Whenever you take damage from a hostile creature while raging, you can use your reaction to reduce the damage by up to half your Barbarian level. The next time you hit a creature with a strength-based attack before the end of your next turn, you can deal additional damage to it equal to the damage you absorbed with this ability.

You can use this ability a number of times per long rest equal to twice your Constitution modifier. Additionally, the first time you are reduced to 0 hit points between long rests, you regain one expended use.

If you are below half health, you can reduce the damage by up to your full Barbarian level. If below one-quart of maximum hit points you can reduce up to twice your Barbarian level worth of damage.

Fast Recovery

Upon making it to 10th level, you have become very accustomed to the cycle of pain and recovery. Whenever you roll hit dice to heal during a short rest, treat any roll of 5 and below as a 6.

Blood Frenzy

At 14 level, you can stimulate extreme ferocity by heavily wounding yourself. As a bonus action, you can sacrifice half your current health to gain advantage on all attacks for one minute, or until your rage ends.