Path of the Pain Siphon

Pain Siphons have the ability to turn potential damage into punishment. While still durable, Pain Siphons are able to channel that damage into their rage, making their attacks hit harder the more damage they take.

Conduit Of Pain

Pain Siphons are known to view pain differently than other barbarians. Their resistance is reactive rather than proactive. 

While Raging, while retaining your original resistances, when you are hit by an attack with a damage type outside the already existing ones you can use your reaction to absorb half the damage and gain resistance to that damage type for the remainder of your Rages duration.

Return to Sender

You can continue to absorb half damage to fuel your. during your rage. keep track of the damage you have absorb. On a bonus action for every five damage you absorb of any specific type, you can choose to remove your absorbed resistance gained from your Conduit of Pain feature and imbue it into your attack.

Every 5 damage absorbed = 1d6 worth of extra damage matching the damage type you absorbed.

The maximum damage you can absorb for this feature is 10 at 3rd, 15 at 9th, and 20 at 15th lvls

Painful insight.

you gain advantage on insight checks as well as a + 10 bonus to the skill

Bond of Pain

As a bonus action, you can choose one allied creature within 30ft of you that you can see.

The chose creature will share in your current resistances, including those from your rage, and Conduit of pain abilities. They do not benefit from you're Return to sender ability but you can continue to absorb the other half of the damage to replenish your reserve and allow them to avoid taking damage all together

you can use this ability a number of times a day equal to your Proficiency bonus rounded down. this ability lasts as long as your rage does.

Painless

When you absorb a damage type, you can expend all the damage you've absorbed using your Conduit of Pain ability to grant yourself immunity to the absorbed damage type for as long as your rage lasts.

Additionally, your attacks deal an extra 1d8 of the absorbed damage type without the need to expend five damage points. If no damage has been absorbed, you deal an extra 1d8 the same damage type as your weapon