Path of the Iron Guardian

Made as deadly defenders eons ago, these fabricated creatures maintain a strong urge to protect those around them. (Warforged Restricted)

Ablative Shielding

Built into your armored form is extra protection that is capable of guarding against superficial damage if brought to bear against incoming blows.

At third level when you take damage, you may use your reaction to have the damage dealt to a pool of hit points equal to five times your barbarian level. Damage done to these hitpoints cannot be reduced by any means, and the hit point pool replenishes at the end of a long rest.  

Super-heated Core

When pretense falls away and an Iron Guardian turns to its true pursuit, the arcane power source deep within its metallic body reaches a nearly intolerable temperature, nearly melting the very being it powers.

At sixth level, while raging your melee attacks gain an extra 1d4+con mod (minimum 1) fire damage (This damage increases to 1d6 at level 10, 1d8 at level 15, and 1d10 at level 20)

Never-ending Vigil

Built as longlasting sentinels, Iron Guardians excel at maintaining surveillance over their chosen charge.

At tenth level you can never be surprised while conscious(including during a warforged's "sentry's rest") and you gain advantage in perception checks to find hiding/hidden creatures. 

Living Fortress

After bearing countless blows across their armored hides, an Iron Guardian learns how to best shield itself from imminent harm.

At fourteenth level, while raging you gain an increase to your armor class and saving throws equal to your rage damage bonus.