Do Half-Human Half-Dragons Exist?
A Demi-Dragon, or Demidragon, is a Dragon-Human Hybrid that looks like a scaly humanoid reptile dragon. In essence a sapient heavy set bipedal Dragon man or woman who can be between 9, and 12 feet tall weighting in at 1-2 tons. These titans of terror have razor sharp teeth, wings to take flight, and can blast forth limited quantities of scorching hot unholy fire from their mouths. It depends on how much fresh meat they’ve eaten recently. Meat that can be any biological entity including humans which they can devour in mere minutes even faster than a Demi-Demon! Realistically as with Werewolves once you see a Demidragon you’re most likely already dead! They can run at speeds topping 100 miles per hour, and rip you in half like a dry twig. Thankfully these horrifying nightmarish monsters are beyond rare, and the odds of you coming across one are astronomical. Most of them are currently thought to exist in the Underworld.
A Demi-Dragon is formed when a Weredragon in their dragon, rather than human, form 
Are Demi-Dragons immortal?
Dragons aren’t Immortal but are thought to live well into the multiple millions of years range. So a Demi-Dragon could probably live to at least a million years old.
Very Interesting. Do they show signs of aging? Are they stronger than werewolves or Yetis?
Signs of aging would probably only occur as they approached the million year old mark. Demi-Dragons are definitely stronger than Werewolves, and Yetis.
In a power comparison to a First or second Generation Vampire, who would be stronger?
Demi-Dragon strength falls in between a First Generation Vampire and a Demi-Demon.