Your Strength score increases by 3 and your Constitution score increases by 2.

Due to their reclusive nature, no one is quite sure how long Earth-Dragonborn live. While they reach full size around 5 years old, their scales seem to stop changing color around 50 years of age. Coming from an ancient earth dragon they don't think about their lifespan death is death.

Mountian Dragonborn stops growing at 12 feet and because of their heavy dense skin, they weigh 600-900 lbs.  Your size is Large

Your base walking speed is 50 feet. 

In honor of the dragon, they descend from they depend on might over magic. You get a +1 to strength 

You can use your action to exhale destructive energy. Your draconic ancestry determines the size, shape, and damage type of the exhalation. When you use your breath weapon, each creature in the area of the exhalation must make a saving throw, the type of which is determined by your draconic ancestry. The DC for this saving throw equals 8 + your Constitution modifier + your proficiency bonus. A creature takes 2d6 damage on a failed save, and half as much damage on a successful one. The damage increases to 3d6 at 6th level, 4d6 at 11th level, and 5d6 at 16th level. After you use your breath weapon, you can’t use it again until you complete a short or long rest.

Mountian Dragonborn can breath molten hot lava as their breath attack. 5 by 30 ft. line ( Dex. save)

You have resistance to fire damage 

While you are not wearing armor, your Armor Class equals 10 + your Constitution modifier +2

You can speak read and write Common, Giant, and Draconic.

Your weight isn't the only crushing thing about you. Whenever you make a Charisma (Intimidation) check against a creature of a size category equal to or smaller than your own, you are considered proficient in the Intimidation skill. If you are already proficient you may add double your proficiency bonus to the check, instead of your normal proficiency bonus.

Status means nothing to them the only battle.

When raging you can use a bonus action to grapple an opponent.