Path of the Pain Bearer

Most living creatures tend to avoid pain the best they can, for it is a sound message of something going wrong and your body or spirit getting destroyed. When confronted to it, savage beasts or trained Battlefolks tend to ignore it, focusing on their next move and attempt to save their life.

You are not like that. Wheter it be by arcane experiment, primal ceremony or ascetic devotion, your body have been profundly transfigured to embrace the physical essence of pain and agony, feeding on it unlike any other creature could. The more you suffer, the stronger you become, pushing your muscles and bones beyond their limits.

Fueled by Pain

At 3rd level, you gain a pool of Pain points. After you take damage, you gain 1 Pain point. You gain an additional point of Pain for each 10 damage you take cumulatively. For example,
you gain 1 Pain point if you take 9 damage, 2 Pain points if you take 14 damage, 3 Pain points if you take 22 damage, etc. You calculate the points you gain after factoring in any resistances you have. If you suffer a critical hit, your fulfill your pool at its maximum.

The maximum number of Pain points you can have is equal to twice your proficiency bonus. The pool is reset to 0 when you get back to your maximum hit points or when you complete a short or a long rest.

You can use your Pain Points in the following ways :

Retribution : When you hit with a melee attack using Strenght while raging, you can spend a number of Pain points to deal extra damage with your attack equal to your Rage damage for each Pain point expended.

Resilience : When you are about to take damage while raging, you can spend a number of Pain points. The damage you take is reduced by an amount equal to your Rage Damage for each pain point you use. This reduction is calculated after any resistances you have.

Pain Catalyst

At 6th level, when a creature that you can see within 30 ft of you is about to take damage, you can use your reaction and spend 3 Pain Points to take said damage in place of the original target.
You can use this reaction a number of time equal to your Constitution Bonus per long rest.
At 16th level, you can perform this reaction one additional time per round by spending 5 Pain points.

Painkiller

Additionnaly at 6th level, your get enough experience with wounds and bruises to know your way around wrapping them up and ease unnecessary amounts of pain. You gain proficiency in the Medicine skill.

Pain is for the living

When you fail on a saving throw, you can expend 4 Pain point to gain a bonus to the roll equal to your Rage Damage, potentially turning the roll to a success.
If you still fail, you must expend 4 additional Pain points and adding the same bonus until you either succeed on the check or run out of Pain points.

You can do this a number of times equal to your proficiency modifier per long rest.

Feed upon Suffering

Once per turn when you hit with a melee weapon attack while raging, you can spend Pain Point to heal 1d4 + your Constitution modifier. Each additional Pain Point you spend after the first adds your Constitution modifier to the healing. You can do that a number of time equal to your Constitution modifier per long rest.

Additionally, when you land a critical hit with a melee weapon attack while raging, each Pain Point you spend in using Retribution deals an additionnal 1d4 damage.

Sharing the Pain

When you damage a creature with an attack while raging, you can use your bonus action and spend 2 Pain Points to link yourself to this creature for 1 minute. You can only have 1 creature linked this way at a time, and any previous link are broken when you create a new one. You can do this a number of time equal to your Constitution modifier per long rest.
If you are about to take damage while raging, you can use your reaction to not gain any Pain Points from this source, and spend 2 Pain Points to Share the Pain : a linked creature within 30 feet of you must make a Constitution saving throw. On a failed save, the linked creature takes the same amount of damage you just took as Necrotic damage, or half on a success, calculated after any resistances you may have. The DC is equal to 8 + your Profiency Modifier + your Constitution Modifier.
Additionally, if the source of damage is a melee weapon attack from a linked creature, you can spend aditionnal Pain Points to give a penalty to it's saving throw equal to your rage damage bonus for each 2 points spend that way.