You are a Humanoid.

You are Medium or Small. You choose the size when you select this race.

Your walking speed is 25 feet.

You are able to discern unnatural objects within rocky terrain giving you advantage on perception checks when in rocky environments. 

You can move across difficult terrain without expending extra movement if you are using your walking speed on the ground or a floor.

You have Resistance to Bludgeoning damage.

As a Bonus Action, you gain Tremorsense with a range of 60 feet for 10 minutes. You must be on a stone surface or touching a stone surface to use this Tremorsense. The stone can be natural or worked.

You can use this Bonus Action a number of times equal to your Proficiency Bonus, and you regain all expended uses when you finish a Long Rest.

Your shell provides you a base AC of 17 (your Dexterity modifier doesn’t affect this number). You can’t wear light, medium, or heavy armor, but if you are using a shield, you can apply the shield’s bonus as normal.

You can contort your body to disguise yourself as a boulder. Creatures have Disadvantage on Perception checks to locate you unless they witnessed your transformation.