Here are the stories behind the 4 ideas I had ... I kinda like that they have some historical background.
1.
Ladon's Lair : Guardian of Hera's golden apple tree. The constellation "Draco" is based upon this dragon
2.
The Dread Biter - Dragon named Nidhoggr who lived at the foot of the world tree, from which all life descends. He bites at the roots of the tree threatening all life. Hence he was known as "The Dread Biter"
3.
Fafnir's Blood - Fafnir was once a humanoid (giant or dwarf, depending on the source) who was transformed into a dragon covered with impenetrable scales. Fafnir's blood was caustic, however, when his blood is tasted it gives one the ability to hear another's thoughts and understand the language of birds.
4.
Jormungandr's Tail - He is noted for his poisonous breath and as the enemy of Thor. Jormungandr lived in the water that surrounds the human world and eventually grew so long he lived all around the world at once and started to eat his own tail.
Descriptions and history copied from
Dragon-Warrior.com.
I am going to vote last so as not to bias the vote. But I will be happy with any of the suggestions presented.
Gary