Sonagon

Summary
Sonagon is a mighty ancient ice dragon, frozen beneath the Lands of Always Winter. After Jon Snow was left for dead by his white walker presuers, his blood soaked the icy grounds and dripped down to Sonagon's frozen body, awakening him from his slumber. Sonagon was continously presueded by the army of the Dead, but with the help of the Three Eyed Raven, Jon Snow and his pets, the Ice Dragon was able to escape their lifeless clutches. Soon after, Sonagon bonded with Jon due to his liniege as a Targaryen as well as someone who has helped him.

Read: Dragons of Ice and Fire.

Statistics
Tier: At least 8-C, possibly 8-A with ice breath

Name: Sonagon, The Beast Beneath, Ice Dragon, The Wildling King's Pet.

Origin: Dragons of Ice and Fire

Gender: Unknown, likely Male

Age: 2000+

Classification: Ice Dragon, Ancient Dragon

Powers and Abilities: Superhuman Physical Characteristics, Longevity, Ice Manipulation(can breath ice and can survive extremely cold temperatures), Enhanced Senses, Telepathy(Can hear Jon's thoughts and mental commands), Flight

Attack Potency: At least Building level (Looked as large if not even larger than Balerion the Black Dread. Easily destroyed small castles and modified boats with just brute force.), possibly Multi-City Block level with ice breath(Turned the Twins into a castle of literal ice. Is believed to be capable of decimating entire kingdoms with relative ease.)

Speed: Superhuman Flight speed (Should be roughly comparable to other dragons.), can go just as fast in water

Lifting Strength: Likely Class K (Managed to drag the body of a whale in cold water.)

Striking Strength: At least Building Class

Durability: At least Building level via sheer size

Stamina: Very High

Range: Hundreds of Meters 

Standard Equipment: None

Intelligence: Extremely High for an animal. Can understand Jon's commands with no problems.

Weaknesses: Relies on his wings for mobility. Some diseases can weaken him.