You speak Draconic, and one language of your choice

You are a Humanoid.

Though Emberborn retain the physical form of their original race, their pact-marked lineage reveals itself through distinct draconic features: a tail and horns that reflect the shape, color, and essence of their Dragon Primogenitor. Their eyes may flicker with emberlight, and subtle signs of their inner flame—such as warmth in their skin or a faint scorched scent—often accompany them.

You are Medium

Your walking speed is 30 ft.

Thanks to the emberfire in your blood, you can see in dim light within 60 feet of you as if it were bright light, and in darkness as if it were dim light. Your emberlit eyes glow faintly in the dark when this trait is active. Often relating to the dragon lineage the color reflects that of the dragon Primogenitor.

You gain horns and a tail that reflect your Dragon Primogenitor in shape and coloration. These are physical and always present.
Your tail may at times move subconsciously, often responding to desires or emotions you are experiencing. 
Your dragon linage grants you fire resistance.

You are permanently changed by the pact. Any children you bear or descendants you leave behind will also be Emberborn of the same lineage. Their original race is overwritten by the pact’s essence. Only the death of the Primogenitor (or divine intervention) can end this bloodline transmission.

If you are not born Emberborn, you may become one by undergoing the Rite of Offering, a powerful ritual that can only be granted by the chosen Primogenitor. This act replaces your previous race, and your body and soul are rewritten in fire.

Once per long rest, when you are reduced to 0 hit points, the ancient flame bound to your soul flares violently. You instead drop to 1 hit point, then immediately regain half your maximum HP. Your eyes blaze with emberlight, your wounds hiss and seal with smoke, and your body refuses the call of death.

"The dragon will not let its chosen fall—not until the fire has nothing left to burn."