Fourthborn - Ironhearts

Fourthborn were quite the sight for the generally larger races that came before them. They were not small, simply shorter, far shorter than the two taller bipedal races before them. They were certainly stout however and had skin not scales, but it was far rougher and thicker than that of the Firstborn . They were gifted with a rather robust physique, somewhat similar to the Thirdborn but their young did not quickly adapt to their abilities like them. They were interesting and unique, and laid about the expectations of the variety that would come from the Borns to come. Fullblood

+1 Strength +1 Wisdom
Heart of Iron: Any test for morale or to resist fear that an Fourthborn must make they gain their proficiency modifier on top of all other modifiers when rolling for the test.
Steel Bones: (Constitution Modifier) times a day for (Proficiency Modifier) minutes a full blooded Iron Heart may harden their body. For this duration they reduce all incoming nonmagical damage by their (Constitution or Wisdom Modifier x (Proficiency Modifier/2)) rounded up. After this moment of hardiness ends they suffer a sudden weariness. Their next turn they have disadvantage on all attacks and every (Proficiency Modifier/2) times of hardening their body they suffer one point of exhaustion.

Halfblood

+1 Wisdom
Solid Stuff: Halfblooded Fourthborn are made of some rather sturdy stuff. At the end of a long rest they garner a temporary health pool that is (Constitution Modifier x Wisdom Modifier x (Proficiency Modifier/2)). Half of whatever was lost of this pool can be recovered after a short rest.
Lost Resonator: Halfblooded perhaps like many of the Borns to come, found some lost ability within the halfbloods, perhaps how in which they found themselves on the surface of Dresslia. Halfblooded Fourthborn add their proficiency modifier on top of all other modifiers when inspecting rocks and metals, as well as when navigating any locale that is underground.